Search

A key component of the Dark Energy Spectroscopic Instrument (DESI) survey validation (SV) is a detailed visual inspection (VI) of the optical spectroscopic data to quantify key survey metrics. In this paper we present results from VI of the quasar survey using deep coadded SV spectra. We show that the majority (~70%) of the main-survey targets are spectroscopically confirmed as quasars, with ~16% galaxies, ~6% stars, and ~8% low-quality spectra lacking reliable features. A non-negligible fraction of the quasars are misidentified by the standard spectroscopic pipeline but we show that the majority can be recovered using post-pipeline "afterburner" quasar-identification approaches. We combine these "afterburners" with our standard pipeline to create a modified pipeline to improve the overall quasar yield. At the depth of the main DESI survey both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km/s) of ~99%; however, the modified pipeline recovers ~94% of the visually inspected quasars, as compared to ~86% from the standard pipeline. We demonstrate that both pipelines achieve an median redshift precision and accuracy of ~100 km/s and ~70 km/s, respectively. We constructed composite spectra to investigate why some quasars are missed by the standard spectroscopic pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of "Seyfert galaxies") and/or dust reddened than the standard-pipeline quasars. We also show example spectra to demonstrate the overall diversity of the DESI quasar sample and provide strong-lensing candidates where two targets contribute to a single spectrum., Comment: Astronomical journal (in press). 26 pages, 15 figures, 9 tables, one of a suite of 8 papers detailing targeting for DESI. Figure data available from Zenodo (see paper for details)

The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect (VI) DESI spectra of approximately 2,500 bright galaxies, 3,500 luminous red galaxies (LRGs), and 10,000 emission line galaxies (ELGs), to obtain robust redshift identifications. We then utilize the VI redshift information to characterize the performance of the DESI operation. Based on the VI catalogs, our results show that the final survey design yields samples of bright galaxies, LRGs, and ELGs with purity greater than $99\%$. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km/s for bright galaxies and ELGs and approximately 40 km/s for LRGs. The average redshift accuracy is within 10 km/s for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show examples of unexpected real astronomical objects, such as Ly$\alpha$ emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases., Comment: 22 pages, 14 figures, 3 tables, one of a suite of 8 papers detailing targeting for DESI. ApJ accepted version with minor textual updates

We present Searches After Gravitational-waves Using ARizona Observatories (SAGUARO), a comprehensive effort dedicated to the discovery and characterization of optical counterparts to gravitational wave (GW) events. SAGUARO utilizes ground-based facilities ranging from 1.5m to 10m in diameter, located primarily in the Northern Hemisphere. We provide an overview of SAGUARO's telescopic resources, pipeline for transient detection, and database for candidate visualization. We describe SAGUARO's discovery component, which utilizes the $5$~deg$^2$ field-of-view optical imager on the Mt. Lemmon 1.5m telescope, reaching limits of $\approx 21.3$~AB mag while rapidly tiling large areas. We also describe the follow-up component of SAGUARO, used for rapid vetting and monitoring of optical candidates. With the onset of Advanced LIGO/Virgo's third observing run, we present results from the first three SAGUARO searches following the GW events S190408an, S190425z and S190426c, which serve as a valuable proof-of-concept of SAGUARO. We triggered and searched 15, 60 and 60 deg$^{2}$ respectively, 17.6, 1.4 and 41.8 hrs after the initial GW alerts. We covered 7.8, 3.0 and 5.1\% of the total probability within the GW event localizations, reaching 3$\sigma$ limits of 19.8, 21.3 and 20.8 AB mag, respectively. Although no viable counterparts associated with these events were found, we recovered 6 known transients and ruled out 5 potential candidates. We also present Large Binocular Telescope spectroscopy of PS19eq/SN2019ebq, a promising kilonova candidate that was later determined to be a supernova. With the ability to tile large areas and conduct detailed follow-up, SAGUARO represents a significant addition to GW counterpart searches., Comment: 16 pages, 7 figures, 1 table. Accepted to ApJL

Following the success of the Plateau de Bure high-z Blue Sequence Survey (PHIBSS), we present the PHIBSS2 legacy program, a survey of the molecular gas properties of star-forming galaxies on and around the star formation main sequence (MS) at different redshifts using NOEMA. This survey significantly extends the existing sample of star-forming galaxies with CO molecular gas measurements, probing the peak epoch of star formation (z=1-1.6) as well as its building-up (z=2-3) and winding-down (z=0.5-0.8) phases. The targets are drawn from the GOODS, COSMOS, and AEGIS deep fields and uniformly sample the MS in the stellar mass (M*) - star formation rate (SFR) plane with log(M*/Msun) = 10-11.8. We describe the survey strategy and sample selection before focusing on the results obtained at z=0.5-0.8, where we report 60 CO(2-1) detections out of 61 targets. We determine their molecular gas masses and separately obtain disc sizes and bulge-to-total (B/T) luminosity ratios from HST I-band images. The median molecular gas-to-stellar mass ratio, gas fraction, and depletion time as well as their dependence with M* and offset from the MS follow published scaling relations for a much larger sample of galaxies spanning a wider range of redshifts. The galaxy-averaged Kennicutt-Schmidt (KS) relation between molecular gas and SFR surface densities is strikingly linear, pointing towards similar star formation timescales within galaxies at any given epoch. In terms of morphology, the molecular gas content, the SFR, the disc stellar mass, and the disc molecular gas fraction do not seem to correlate with B/T and the stellar surface density, which suggests an ongoing supply of fresh molecular gas to compensate for the build-up of the bulge. Our measurements do not yield any significant variation of the depletion time with B/T and hence no strong evidence for morphological quenching within the scatter of the MS., Comment: Accepted for publication in A&A (28 pages, 9 figures, 4 tables)

A massive galaxy cluster can serve as a magnifying glass for distant stellar populations, with strong gravitational lensing exposing details in the lensed background galaxies that would otherwise be undetectable. The MACS J0416.1-2403 cluster (hereafter MACS0416) is one of the most efficient lenses in the sky, and in 2014 it was observed with high-cadence imaging from the Hubble Space Telescope (HST). Here we describe two unusual transient events that appeared behind MACS0416 in a strongly lensed galaxy at redshift $z = 1.0054 \pm 0.0002$. These transients---designated HFF14Spo-NW and HFF14Spo-SE and collectively nicknamed "Spock"---were faster and fainter than any supernova (SN), but significantly more luminous than a classical nova. They reached peak luminosities of $\sim10^{41}$ erg s$^{-1}$ ($M_{\rm AB} < -14$ mag) in 5 rest-frame days, then faded below detectability in roughly the same time span. Models of the cluster lens suggest that these events may be spatially coincident at the source plane, but are most likely not temporally coincident. We find that HFF14Spo can be explained as a luminous blue variable (LBV), a recurrent nova (RN), or a pair of stellar microlensing events. To distinguish between these hypotheses will require a clarification of the positions of nearby critical curves, along with high-cadence monitoring of the field that could detect new transient episodes in the host galaxy., Comment: 14 pages (Main text + figures) + 40 pages (Methods, References and Supplementary Info)

The reionization of the Universe is one of the most important topics of present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the HI ionizing background at z~3. We aim at measuring the Lyman continuum escape fraction, which is one of the key parameters to compute the contribution of star-forming galaxies to the UV background. We have used ultra-deep U-band imaging (U=30.2mag at 1sigma) by LBC/LBT in the CANDELS/GOODS-North field, as well as deep imaging in COSMOS and EGS fields, in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27L*), while for the faint population (L=0.2L*) the limit to the escape fraction is ~10%. We have computed the contribution of star-forming galaxies to the observed UV background at z~3 and we have found that it is not enough to keep the Universe ionized at these redshifts, unless their escape fraction increases significantly (>10%) at low luminosities (M1500>-19). We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental to measure the Lyman continuum escape fraction down to faint magnitudes (M1500~-16) which are inaccessible with the present instrumentation on blank fields., Comment: Accepted for publication in A&A, 16 pages, 6 figures

This paper provides an update of our previous scaling relations (Genzel et al.2015) between galaxy integrated molecular gas masses, stellar masses and star formation rates, in the framework of the star formation main-sequence (MS), with the main goal to test for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ~1mm dust photometry, in a large sample of 1444 star forming galaxies (SFGs) between z=0 and 4. The sample covers the stellar mass range log(M*/M_solar)=9.0-11.8, and star formation rates relative to that on the MS, delta_MS=SFR/SFR(MS), from 10^{-1.3} to 10^{2.2}. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t_depl, defined as the ratio of molecular gas mass to star formation rate, scales as (1+z)^{-0.6}x(delta_MS)^{-0.44}, and is only weakly dependent on stellar mass. The ratio of molecular-to-stellar mass mu_gas depends on (1+z)^{2.5}x (delta_MS)^{0.52}x(M*)^{-0.36}, which tracks the evolution of the specific star formation rate. The redshift dependence of mu_gas requires a curvature term, as may the mass-dependences of t_depl and mu_gas. We find no or only weak correlations of t_depl and mu_gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high-z., Comment: Now accepted by ApJ; Figures and tables have been updated, and an appendix has been added

We present $\simeq$0$.\!\!^{\prime\prime}4$-resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at $z = 1.3-3.0$. These galaxies are selected from sensitive, blank-field surveys of the $2' \times 2'$ Hubble Ultra-Deep Field at $\lambda = 5$ cm and 1.3 mm using the Karl G. Jansky Very Large Array (VLA) and Atacama Large Millimeter/submillimeter Array (ALMA). They have star-formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at $z \sim 2$. Morphological classification performed on spatially-resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGN), thereby representing a diversity of $z \sim 2$ SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of $4.2 \pm 1.8$ kpc. This provides direct evidence for galaxy-wide star formation in distant, blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M$_{\odot}$yr$^{-1}$kpc$^{-2}$, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGN, which are found to be co-spatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies whose SFRs are $3-8$ times larger, providing a constraint on the characteristic SFR ($\sim300$ M$_{\odot}$yr$^{-1}$) above which a significant population of more compact star-forming galaxies appears to emerge., Comment: 11 pages, 4 figures, accepted for publication in ApJ

We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe), and we find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, we measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it would have an ejecta mass of 20+-5 solar masses. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex and <8.4 dex, respectively) near the explosion site., Comment: Submitted to ApJ; 26 pages

We present the first year of Hubble Space Telescope imaging of the unique supernova (SN) 'Refsdal', a gravitationally lensed SN at z=1.488$\pm$0.001 with multiple images behind the galaxy cluster MACS J1149.6+2223. The first four observed images of SN Refsdal (images S1-S4) exhibited a slow rise (over ~150 days) to reach a broad peak brightness around 20 April, 2015. Using a set of light curve templates constructed from SN 1987A-like peculiar Type II SNe, we measure time delays for the four images relative to S1 of 4$\pm$4 (for S2), 2$\pm$5 (S3), and 24$\pm$7 days (S4). The measured magnification ratios relative to S1 are 1.15$\pm$0.05 (S2), 1.01$\pm$0.04 (S3), and 0.34$\pm$0.02 (S4). None of the template light curves fully captures the photometric behavior of SN Refsdal, so we also derive complementary measurements for these parameters using polynomials to represent the intrinsic light curve shape. These more flexible fits deliver fully consistent time delays of 7$\pm$2 (S2), 0.6$\pm$3 (S3), and 27$\pm$8 days (S4). The lensing magnification ratios are similarly consistent, measured as 1.17$\pm$0.02 (S2), 1.00$\pm$0.01 (S3), and 0.38$\pm$0.02 (S4). We compare these measurements against published predictions from lens models, and find that the majority of model predictions are in very good agreement with our measurements. Finally, we discuss avenues for future improvement of time delay measurements -- both for SN Refsdal and for other strongly lensed SNe yet to come., Comment: 19 pages, 9 figures; ApJ in press; v4: corrected layout errors and bibliography arXiv identifiers

In Hubble Space Telescope (HST) imaging taken on 10 November 2014, four images of supernova (SN) "Refsdal" (redshift z=1.49) appeared in an Einstein-cross--like configuration (images S1-S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z=0.54). Almost all lens models of the cluster have predicted that the SN should reappear within a year in a second host-galaxy image created by the cluster's potential. In HST observations taken on 11 December 2015, we find a new source at the predicted position of the new image of SN Refsdal approximately 8" from the previous images S1-S4. This marks the first time the appearance of a SN at a particular time and location in the sky was successfully predicted in advance! We use these data and the light curve from the first four observed images of SN Refsdal to place constraints on the relative time delay and magnification of the new image (SX), compared to images S1-S4. This enables us, for the first time, to test "blind" lens model predictions of both magnifications and time delays for a lensed SN. We find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrates the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty. From planned HST photometry, we expect to reach a precision of 1-2% on the time delay between S1-S4 and SX., Comment: Accepted ApJL version

We derive the total cold gas, atomic hydrogen, and molecular gas masses of approximately 24 000 galaxies covering four decades in stellar mass at redshifts 0.5 < z < 3.0, taken from the CANDELS survey. Our inferences are based on the inversion of a molecular hydrogen based star formation law, coupled with a prescription to separate atomic and molecular gas. We find that: 1) there is an increasing trend between the inferred cold gas (HI and H2), HI, and H2 mass and the stellar mass of galaxies down to stellar masses of 10^8 Msun already in place at z = 3; 2) the molecular fractions of cold gas increase with increasing stellar mass and look-back time; 3) there is hardly any evolution in the mean HI content of galaxies at fixed stellar mass; 4) the cold gas fraction and relative amount of molecular hydrogen in galaxies decrease at a relatively constant rate with time, independent of stellar mass; 5) there is a large population of low-stellar mass galaxies dominated by atomic gas. These galaxies are very gas rich, but only a minor fraction of their gas is molecular; 6) the ratio between star-formation rate (SFR) and inferred total cold gas mass (HI + H2) of galaxies (i.e., star-formation efficiency; SFE) increases with star-formation at fixed stellar masses. Due to its simplicity, the presented approach is valuable to assess the impact of selection biases on small samples of directly-observed gas masses and to extend scaling relations down to stellar mass ranges and redshifts that are currently difficult to probe with direct measurements of gas content., Comment: Accepted for publication in MNRAS. 22 pages, 18 figures. Data products are available at http://www.eso.org/~gpopping/Gergo_Poppings_Homepage/Data.html

We present a complete census of all Herschel-detected sources within the six massive lensing clusters of the HST Frontier Fields (HFF). We provide a robust legacy catalogue of 263 sources with Herschel fluxes, primarily based on imaging from the Herschel Lensing Survey (HLS) and PEP/HerMES Key Programmes. We optimally combine Herschel, Spitzer and WISE infrared (IR) photometry with data from HST, VLA and ground-based observatories, identifying counterparts to gain source redshifts. For each Herschel-detected source we also present magnification factor (mu), intrinsic IR luminosity and characteristic dust temperature, providing a comprehensive view of dust-obscured star formation within the HFF. We demonstrate the utility of our catalogues through an exploratory overview of the magnified population, including more than 20 background sub-LIRGs unreachable by Herschel without the assistance gravitational lensing., Comment: 21 pages (+10 pages of tables), 18 figures, 9 tables. Published in MNRAS. All imaging, catalogues and SEDs are available on Rainbow (https://rainbowx.fis.ucm.es)

We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) project. We combine the effort from ten different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ~80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age < 100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for < 20 Myr sources) if nebular contribution is ignored., Comment: Accepted for publication by ApJ. Replaced to match the final version (two tables and one figure added in the appendix)

Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present day stellar masses near M*, at 5x10^10 Msol (MW-mass) and 10^11 Msol (M31-mass). We study the typical progenitors of these galaxies using ZFOURGE, a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z~3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star-formation rates combining our deep multiwavelength imaging with near-IR HST imaging from CANDELS, and far-IR imaging from GOODS-H and CANDELS-H. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages, to redder dust-obscured IR-luminous galaxies in intermediate stages, and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of 2-3 lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star-formation in present-day M* galaxies requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and star-formation rates imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z~0 and are strongly anticorrelated with an increase in the S\'ersic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star-formation efficiency., Comment: Accepted for publication in ApJ; 25 pages, emulateapj format

We combine molecular gas masses inferred from CO emission in 500 star forming galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other surveys, with gas masses derived from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion time scale (tdepl) and gas to stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence with redshift, specific star formation rate (sSFR) and stellar mass (M*). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO-H2 mass conversion factor varies little within 0.6dex of the main sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M* are driven by the flattening of the SFR-M* relation. Throughout the redshift range probed a larger sSFR at constant M* is due to a combination of an increasing gas fraction and a decreasing depletion time scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine Mmolgas with an accuracy of 0.1dex in relative terms, and 0.2dex including systematic uncertainties., Comment: ApJ accepted

We present direct constraints on the CO luminosity function at high redshift and the resulting cosmic evolution of the molecular gas density, $\rho_{\rm H2}$(z), based on a blind molecular line scan in the Hubble Deep Field North (HDF-N) using the IRAM Plateau de Bure Interferometer. Our line scan of the entire 3mm window (79-115 GHz) covers a cosmic volume of ~7000 Mpc$^3$, and redshift ranges z<0.45, 1.012. We use the rich multiwavelength and spectroscopic database of the HDF-N to derive some of the best constraints on CO luminosities in high redshift galaxies to date. We combine the blind CO detections in our molecular line scan (presented in a companion paper) with stacked CO limits from galaxies with available spectroscopic redshifts (slit or mask spectroscopy from Keck and grism spectroscopy from HST) to give first blind constraints on high-z CO luminosity functions and the cosmic evolution of the H2 mass density $\rho_{\rm H2}$(z) out to redshifts z~3. A comparison to empirical predictions of $\rho_{\rm H2}$(z) shows that the securely detected sources in our molecular line scan already provide significant contributions to the predicted $\rho_{\rm H2}$(z) in the redshift bins ~1.5 and ~2.7. Accounting for galaxies with CO luminosities that are not probed by our observations results in cosmic molecular gas densities $\rho_{\rm H2}$(z) that are higher than current predictions. We note however that the current uncertainties (in particular the luminosity limits, number of detections, as well as cosmic volume probed) are significant, a situation that is about to change with the emerging ALMA observatory., Comment: Accepted for publication in ApJ

We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z<0.45, 12. We reach a CO detection limit that is deep enough to detect essentially all z>1 CO lines reported in the literature so far. We have developed and applied different line searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ~2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available SEDs. Two secure CO detections in our scan are identified with star-forming galaxies at z=1.784 and at z=2.047. These galaxies have colors consistent with the `BzK' color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF850.1 at z=5.183. We consider an additional 9 line candidates as high quality. Our observations also provide a deep 3mm continuum map (1-sigma noise level = 8.6 $\mu$Jy/beam). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to <50% of the SFR density at 1

Out of several dozen z > 7 candidate galaxies observed spectroscopically, only five have been confirmed via Lyman-alpha emission, at z=7.008, 7.045, 7.109, 7.213 and 7.215. The small fraction of confirmed galaxies may indicate that the neutral fraction in the intergalactic medium (IGM) rises quickly at z > 6.5, as Lyman-alpha is resonantly scattered by neutral gas. However, the small samples and limited depth of previous observations makes these conclusions tentative. Here we report the results of a deep near-infrared spectroscopic survey of 43 z > 6.5 galaxies. We detect only a single galaxy, confirming that some process is making Lyman-alpha difficult to detect. The detected emission line at 1.0343 um is likely to be Lyman-alpha emission, placing this galaxy at a redshift z = 7.51, an epoch 700 million years after the Big Bang. This galaxy's colors are consistent with significant metal content, implying that galaxies become enriched rapidly. We measure a surprisingly high star formation rate of 330 Msol/yr, more than a factor of 100 greater than seen in the Milky Way. Such a galaxy is unexpected in a survey of our size, suggesting that the early universe may harbor more intense sites of star-formation than expected., Comment: To be published in Nature on 24 October. Under press embargo until 1pm EDT on 23 October. 12 pages, 8 figures, 4 tables (including supplementary information)

Based on high-resolution, spatially resolved data of 10 z~2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGN), shocks and photoionization. We explore how these spatially-resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the `composite' region of the z~0 [NII]/Ha versus [OIII]/Hb diagnostic (BPT) diagram, between star-forming galaxies and those with AGN. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from enhanced ionization parameter as compared with HII regions in normal local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [OIII]/Hb versus stellar mass plane, does not properly separate z~2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z~2 mass-metallicity relation (i.e. to the mass they would have at z~0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [NII]/Ha are more biased by shocks and AGN at high-z than the [OIII]/Hb/[NII]/Ha calibration., Comment: 19 pages, 17 figures, submitted to ApJ

We report matched resolution, imaging spectroscopy of the CO J=3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the H-alpha line (with LUCI at the Large Binocular Telescope)in the massive z=1.53 main-sequence galaxy EGS 13011166, as part of the "Plateau de Bure high-z, blue sequence survey (PHIBSS). We combine these data with HST V-J-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution, and peaks in an obscured, star forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a 'mixed' extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation depends strongly on the adopted extinction model and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model we find a near linear slope., Comment: submitted to the Astrophysical Journal

We present a study of the prevalence, strength, and kinematics of ultraviolet FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected from the DEEP2 survey. We find FeII* emission in composite spectra assembled on the basis of different galaxy properties, indicating that FeII* emission is prevalent at z = 1. In these composites, FeII* emission is observed at roughly the systemic velocity. At z = 1, we find that the strength of FeII* emission is most strongly modulated by dust attenuation, and is additionally correlated with redshift, star-formation rate, and [OII] equivalent width, such that systems at higher redshifts with lower dust levels, lower star-formation rates, and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII emission in at least 15% of the individual spectra and we find that objects showing stronger MgII emission have higher specific star-formation rates, smaller [OII] linewidths, larger [OII] equivalent widths, lower dust attenuations, and lower stellar masses than the sample as a whole. MgII emission strength exhibits the strongest correlation with specific star-formation rate, although we find evidence that dust attenuation and stellar mass also play roles in the regulation of MgII emission. Future integral field unit observations of the spatial extent of FeII* and MgII emission in galaxies with high specific star-formation rates, low dust attenuations, and low stellar masses will be important for probing the morphology of circumgalactic gas., Comment: 29 pages, 22 figures, 2 tables; accepted to ApJ

Massive galaxies in the distant Universe form stars at much higher rates than today. Although direct resolution of the star forming regions of these galaxies is still a challenge, recent molecular gas observations at the IRAM Plateau de Bure interferometer enable us to study the star formation efficiency on subgalactic scales around redshift z = 1.2. We present a method for obtaining the gas and star formation rate (SFR) surface densities of ensembles of clumps composing galaxies at this redshift, even though the corresponding scales are not resolved. This method is based on identifying these structures in position-velocity diagrams corresponding to slices within the galaxies. We use unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of four massive star forming distant galaxies - EGS13003805, EGS13004291, EGS12007881, and EGS13019128 in the AEGIS terminology - to determine the gas and SFR surface densities of the identifiable ensembles of clumps that constitute them. The integrated CO line luminosity is assumed to be directly proportional to the total gas mass, and the SFR is deduced from the [OII] line. We identify the ensembles of clumps with the angular resolution available in both CO and [OII] spectroscopy; i.e., 1-1.5". SFR and gas surface densities are averaged in areas of this size, which is also the thickness of the DEEP2 slits and of the extracted IRAM slices, and we derive a spatially resolved Kennicutt-Schmidt (KS) relation on a scale of ~8 kpc. The data generally indicates an average depletion time of 1.9 Gyr, but with significant variations from point to point within the galaxies., Comment: 6 pages, 4 figures, 2 tables, accepted by Astronomy and Astrophysics

We present a multi-wavelength study of a 3.6 $\mu$m-selected galaxy sample in the Extended Groth strip. The sample is complete for galaxies with stellar mass $>10^{9.5}$ \Msun and redshift $0.4}3\sigma$ errors) is about 3.5%. A new method of validation based on pair statistics confirms the estimate of standard deviation even for galaxies lacking spectroscopic redshifts. Basic galaxy properties measured include rest-frame $U-B$ colors, $B$- and $K$-band absolute magnitudes, and stellar masses. We divide the sample into quiescent and star-forming galaxies according to their rest-frame $U-B$ colors and 24 to 3.6 \micron\ flux density ratios and derive rest $K$-band luminosity functions and stellar mass functions for quiescent, star forming, and all galaxies. The results show that massive, quiescent galaxies were in place by $z\approx1$, but lower mass galaxies generally ceased their star formation at later epochs., Comment: 64 pages, 24 figures

We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in normal star forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z~1.2 and 2.2, with log(M*(M_solar))>10.4 and log(SFR(M_solar/yr))>1.5. Including a correction for the incomplete coverage of the M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z~1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular gas - star formation relation for the z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M*, gas fractions correlate strongly with the specific star formation rate. The variation of specific star formation rate between z~0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas., Comment: Submitted to the Astrophysical Journal; 14 figures

We present spectroscopic observations in the rest-frame optical and near- to mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample was selected to represent pure, actively star-forming systems, absent of active galactic nuclei. The large lensing magnifications result in high signal-to-noise spectra that can probe faint IR recombination lines, including Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three lensed galaxies with similar suites of unpublished data and observations from the literature, resulting in the final sample of seven galaxies. We use the IR recombination lines in conjunction with H-alpha observations to probe the extinction, Av, of these systems, as well as testing star formation rate (SFR) indicators against the SFR measured by fitting spectral energy distributions to far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger than previously known for a similar range of IR luminosities at these redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of extinction in the most IR luminous galaxies. We also measure extinction by comparing SFR estimates from optical emission lines with those from far-IR measurements. The comparison of results from these two independent methods indicates a large variety of dust distribution scenarios at 1 < z < 3. Without correcting for dust extinction, the H-alpha SFR indicator underestimates the SFR; the size of the necessary correction depends on the IR luminosity and dust distribution scenario. Individual SFR estimates based on the 6.2 micron PAH emission line luminosity do not show a systematic discrepancy with extinction, although a considerable, ~0.2 dex scatter is observed., Comment: Accepted for publication in The Astrophysical Journal; 14 pages, 8 figures

We present the Arizona CDFS Environment Survey (ACES), a recently-completed spectroscopic redshift survey of the Chandra Deep Field South (CDFS) conducted using IMACS on the Magellan-Baade telescope. In total, the survey targeted 7277 unique sources down to a limiting magnitude of R = 24.1, yielding 5080 secure redshifts across the ~30' x 30' extended CDFS region. The ACES dataset delivers a significant increase to both the spatial coverage and the sampling density of the spectroscopic observations in the field. Combined with previously-published, spectroscopic redshifts, ACES now creates a highly-complete survey of the galaxy population at R < 23, enabling the local galaxy density (or environment) on relatively small scales (~1 Mpc) to be measured at z < 1 in one of the most heavily-studied and data-rich fields in the sky. Here, we describe the motivation, design, and implementation of the survey and present a preliminary redshift and environment catalog. In addition, we utilize the ACES spectroscopic redshift catalog to assess the quality of photometric redshifts from both the COMBO-17 and MUSYC imaging surveys of the CDFS., Comment: resubmitted to MNRAS; 12 pages, 12 figures, and 3 tables; updated redshift catalog available at http://mur.ps.uci.edu/~cooper/ACES/

We discuss the structural and morphological properties of galaxies in a z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (< 1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a result the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z~1.6 to the present, growing as (1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seems to have caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower subsequent growth at z<1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z<1 clusters., Comment: Accepted for publication in ApJ. 14 pages in emulateapj format. Replacement includes improvements from referee report, and updates and additions to references

We identify an abundant population of extreme emission line galaxies (EELGs) at redshift z~1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). 69 EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broad-band magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines -- with rest-frame equivalent widths ~1000\AA -- in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with 10^8 Msol in stellar mass, undergoing an enormous starburst phase with M_*/(dM_*/dt) of only ~15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the co-moving number density (3.7x10^-4 Mpc^-3) can produce in ~4 Gyr much of the stellar mass density that is presently contained in 10^8-10^9 Msol dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z>1., Comment: accepted for publication in ApJ; 10 pages; 6 figures; 1 table

We demonstrate estimating the total infrared luminosity, LIR, and star formation rates (SFRs) of star-forming galaxies at redshift 0 < z < 2.8 from single-band 24 micron observations, using local spectral energy distributions (SED) templates without introducing additional free parameters. Our method is based on characterizing the SEDs of galaxies as a function of their LIR surface density, which is motivated by the indications that the majority of IR luminous star-forming galaxies at 1 < z < 3 have extended star-forming regions, in contrast to the strongly nuclear concentrated, merger-induced starbursts in local luminous and ultraluminous IR galaxies. We validate our procedure for estimating LIR by comparing the resulting LIRs with those measured from far-IR observations at 0 < z < 2.8. AGNs were excluded using X-ray and 3.6-8.0 micron observations, which are generally available in deep cosmological survey fields. The Gaussian fits to the distribution of the discrepancies between the LIR measurements from single-band 24 micron and Herschel observations have sigma < 0.1 dex, with ~10% of objects disagreeing by more than 0.2 dex. Since the 24 micron estimates are based on SEDs for extended galaxies, this agreement suggests that ~90% of IR galaxies at high z are indeed much more physically extended than local counterparts of similar LIR, consistent with recent independent studies of the fractions of galaxies forming stars in the main-sequence and starburst modes, respectively. Because we have not introduced empirical corrections to enhance these estimates, in principle, our method should be applicable to lower luminosity galaxies. This will enable use of the 21 micron band of the Mid-Infrared Instrument (MIRI) on board the JWST to provide an extremely sensitive tracer of obscured SFR in individual star-forming galaxies across the peak of the cosmic star formation history., Comment: 17 pages, 7 figures, ApJ accepted

We use the first systematic samples of CO millimeter emission in z>1 'main-sequence' star forming galaxies (SFGs) to study the metallicity dependence of the conversion factor {\alpha}CO, from CO line luminosity to molecular gas mass. The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is ~1 Gyr-1 for near-solar metallicity galaxies with stellar masses above M_S~1e11 M_sun. In this regime the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density, or redshift between z~0 and 2. Below M_S the depletion rate increases rapidly with decreasing metallicity. We argue that this trend is not caused by starburst events, by changes in the physical parameters of the molecular clouds, or by the impact of the fundamental metallicity-SFR-stellar mass relation. A more probable explanation is that the conversion factor is metallicity dependent and that star formation can occur in 'CO-dark' gas. The trend is also expected theoretically from the effect of enhanced photodissociation of CO by ultraviolet radiation at low metallicity. From the available z~0 and z~1-3 samples we constrain the slope of the log({\alpha}CO) -log (metallicity) relation to range between -1 and -2, fairly insensitive to the assumed slope of the gas-star formation rate relation. Because of the lower metallicities near the peak of the galaxy formation activity at z~1-2 compared to z~0, we suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M_S., Comment: ApJ in press

We analyze the association of galaxies to Lya and OVI absorption, the most commonly detected transitions in the low-z intergalactic medium (IGM), in the fields of 14 quasars with z_em = 0.06-0.57. Confirming previous studies, we observe a high covering fraction for Lya absorption to impact parameter rho = 300kpc: 33/37 of our L>0.01L* galaxies show Lya equivalent width W_Lya>50mA. Galaxies of all luminosity L>0.01L* and spectral type are surrounded by a diffuse and ionized circumgalactic medium (CGM), whose baryonic mass is estimated at ~10^(10.5 +/- 0.3) Msun for a constant N_H. The virialized halos and extended CGM of present-day galaxies are responsible for most strong Lya absorbers (W_Lya > 300mA) but cannot reproduce the majority of observed lines in the Lya forest. We conclude that the majority of Lya absorption with W_Lya=30-300mA occurs in the cosmic web predicted by cosmological simulations and estimate a characteristic width for these filaments of ~400kpc. Regarding OVI, we observe a near unity covering fraction to rho=200kpc for L>0.1L* galaxies and to rho = 300kpc for sub-L* (0.1 L* 70mA) arise in the virialized halos of L>0.1L* galaxies. Unlike Lya, the weaker OVI systems (W_OVI~30mA) arise in the extended CGM of sub-L* galaxies. The majority of OVI gas observed in the low-z IGM is associated with a diffuse medium surrounding individual galaxies with L~0.3L*, and rarely originates in the so-called warm-hot IGM (WHIM) predicted by cosmological simulations., Comment: Submitted to the Astrophysical Journal; 26 pages, 9 figures. See http://www.ucolick.org/~xavier/WFCCDOVI/index.html for more

We publish the survey for galaxies in 20 fields containing ultraviolet bright quasars (with z_em 0.1 to 0.5) that can be used to study the association between galaxies and absorption systems from the low-z intergalactic medium (IGM). The survey is magnitude limited (R~19.5 mag) and highly complete out to 10' from the quasar in each field. It was designed to detect dwarf galaxies (L ~ 0.1 L*) at an impact parameter rho 1Mpc (z=0.1) from a quasar. The complete sample (all 20 fields) includes R-band photometry for 84718 sources and confirmed redshifts for 2800 sources. This includes 1198 galaxies with 0.005 < z < (z_em - 0.01) at a median redshift of 0.18, which may associated with IGM absorption lines. All of the imaging was acquired with cameras on the Swope 40" telescope and the spectra were obtained via slitmask observations using the WFCCD spectrograph on the Dupont 100" telescope at Las Campanas Observatory (LCO). This paper describes the data reduction, imaging analysis, photometry, and spectral analysis of the survey. We tabulate the principal measurements for all sources in each field and provide the spectroscopic dataset online., Comment: Accepted to the Astrophysical Journal Supplements; 20 pages, only 6 figures shown in this version. See http://www.ucolick.org/~xavier/WFCCDOVI/index.html for a full-length manuscript and other supportive material

The "Extreme starbursts in the local universe" workshop was held at the Insituto de Astrofisica de Andalucia in Granada, Spain on 21-25 June 2010. Bearing in mind the advent of a new generation of facilities such as JWST, Herschel, ALMA, eVLA and eMerlin, the aim of the workshop was to bring together observers and theorists to review the latest results. The purpose of the workshop was to address the following issues: what are the main modes of triggering extreme starbursts in the local Universe? How efficiently are stars formed in extreme starbursts? What are the star formation histories of local starburst galaxies? How well do the theoretical simulations model the observations? What can we learn about starbursts in the distant Universe through studies of their local counterparts? How important is the role of extreme starbursts in the hierarchical assembly of galaxies? How are extreme starbursts related to the triggering of AGN in the nuclei of galaxies? Overall, 41 talks and 4 posters with their corresponding 10 minutes short talks were presented during the workshop. In addition, the workshop was designed with emphasis on discussions, and therefore, there were 6 discussion sessions of up to one hour during the workshop. Here is presented a summary of the purposes of the workshop as well as a compilation of the abstracts corresponding to each of the presentations. The summary and conclusions of the workshop along with a description of the future prospects by Sylvain Veilleux can be found in the last section of this document. A photo of the assistants is included., Comment: workshop

We use the first systematic data sets of CO molecular line emission in z~1-3 normal star forming galaxies for a comparison of the dependence of galaxy-averaged star formation rates on molecular gas masses at low and high redshifts, and in different galactic environments. Although the current high-z samples are still small and biased toward the luminous and massive tail of the actively star-forming 'main-sequence', a fairly clear picture is emerging. Independent of whether galaxy integrated quantities or surface densities are considered, low- and high-z SFG galaxy populations appear to follow similar molecular gas-star formation relations with slopes 1.1 to 1.2. The gas-depletion time scale in these SFGs grows from 0.5 Gyrs at z~2 to 1.5 Gyrs at z~0. Because star formation depletion times are significantly smaller than the Hubble time at all redshifts sampled, star formation rates and gas fractions are set by the balance between gas accretion from the halo and stellar feedback. In contrast, very luminous gas rich major mergers at both low-z and high-z produce on average 4 to10 times more far-infrared luminosity per unit gas mass. Only some fraction of this difference can be explained by uncertainties in gas-mass or luminosity estimators; much of it must be intrinsic. The most likely interpretation is that the star formation relation is driven by global dynamical effects. For a given mass, the more compact merger systems produce stars more rapidly because their gas clouds are more compressed with shorter dynamical times, so that they churn more quickly through the available gas reservoir than the typical normal disk galaxies. When the dependence on galactic dynamical time scale is explicitly included, disk galaxies and mergers appear to follow similar gas to star-formation relations. The mergers may be forming stars at slightly higher efficiencies than the disks., Comment: accepted for publication in MNRAS

Stars form from cold molecular interstellar gas. Since this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more gas rich. Molecular gas observations in the distant Universe have so far been largely restricted to very luminous, rare objects, including mergers and quasars. Here we report the results of a systematic survey of molecular gas in samples of typical massive star forming galaxies at ~1.2 and 2.3, when the Universe was 40% and 24% of its current age. Our measurements provide empirical evidence that distant star forming galaxies indeed were gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z= 2.3 and z=1.2 is ~44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z~2 and 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies., Comment: To Appear in Nature Feb 11, 2010; Supplementary Information included here

This paper describes the Maryland-Magellan Tunable Filter (MMTF) on the Magellan-Baade 6.5-meter telescope. MMTF is based on a 150-mm clear aperture Fabry-Perot (FP) etalon that operates in low orders and provides transmission bandpass and central wavelength adjustable from ~5 to ~15 A and from ~5000 to over ~9200 A, respectively. It is installed in the Inamori Magellan Areal Camera and Spectrograph (IMACS) and delivers an image quality of ~0.5" over a field of view of 27' in diameter (monochromatic over ~10'). This versatile and easy-to-operate instrument has been used over the past three years for a wide variety of projects. This paper first reviews the basic principles of FP tunable filters, then provides a detailed description of the hardware and software associated with MMTF and the techniques developed to observe with this instrument and reduce the data. The main lessons learned in the course of the commissioning and implementation of MMTF are highlighted next, before concluding with a brief outlook on the future of MMTF and of similar facilities which are soon coming on line., Comment: 38 pages, 12 figures, 3 tables, now accepted for publication to the Astronomical Journal

In this paper we address the consumption of energy by astronomers while performing their professional duties. Although we find that astronomy uses a negligible fraction of the US energy budget, the rate at which energy is consumed by an average astronomer is similar to that of a typical high-flying businessperson. We review some of the ways in which astronomers are already acting to reduce their energy consumption. In the coming decades, all citizens will have to reduce their energy consumption to conserve fossil fuel reserves and to help avert a potentially catastrophic change in the Earth's climate. The challenges are the same for astronomers as they are for everyone: decreasing the distances we travel and investing in energy-efficient infrastructure. The high profile of astronomy in the media, and the great public interest in our field, can play a role in promoting energy-awareness to the wider population. Our specific recommendations are therefore to 1) reduce travel when possible, through efficient meeting organization, and by investing in high-bandwidth video conference facilities and virtual-world software, 2) create energy-efficient observatories, computing centers and workplaces, powered by sustainable energy resources, and 3) actively publicize these pursuits., Comment: "State of the Profession" white paper submitted to the 2010 Astronomy & Astrophysics Decadal Survey. Add your thoughts to the wiki at http://low-energy-astro.physics.ucsb.edu

Great strides have been made in the last two decades in determining how galaxies evolve from their initial dark matter seeds to the complex structures we observe at z=0. The role of mergers has been documented through both observations and simulations, numerous satellites that may represent these initial dark matter seeds have been discovered in the Local Group, high redshift galaxies have been revealed with monstrous star formation rates, and the gaseous cosmic web has been mapped through absorption line experiments. Despite these efforts, the dark matter simulations that include baryons are still unable to accurately reproduce galaxies. One of the major problems is our incomplete understanding of how a galaxy accretes its baryons and subsequently forms stars. Galaxy formation simulations have been unable to accurately represent the required gas physics on cosmological timescales, and observations have only just begun to detect the star formation fuel over a range of redshifts and environments. How galaxies obtain gas and subsequently form stars is a major unsolved, yet tractable problem in contemporary extragalactic astrophysics. In this paper we outline how progress can be made in this area in the next decade., Comment: 8 pages, Science white paper for the Astro2010 Decadal Survey, 2 color figures

There is a large observational scatter toward low velocities in the stellar mass Tully-Fisher relation if disturbed and compact objects are included. However, this scatter can be eliminated if one replaces rotation velocity with $\rm S_{\rm 0.5}$, a quantity that includes a velocity dispersion term added in quadrature with the rotation velocity. In this work we use a large suite of hydrodynamic N-body galaxy merger simulations to explore a possible mechanism for creating the observed relations. Using mock observations of the simulations, we test for the presence of observational effects and explore the relationship between $\rm S_{\rm 0.5}$ and intrinsic properties of the galaxies. We find that galaxy mergers can explain the scatter in the TF as well as the tight $\rm S_{\rm 0.5}$-stellar mass relation. Furthermore, $\rm S_{\rm 0.5}$ is correlated with the total central mass of a galaxy, including contributions due to dark matter., Comment: ApJ accepted