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In this paper we investigate the stellar populations and star formation histories of 235 active galactic nuclei (AGN)-host dwarf galaxies, consisting of four samples identified separately with different methods (i.e., radio, X-ray, mid-IR and variability), utilizing the synthesis code STARLIGHT and spectra from the Sloan Digital Sky Survey (SDSS) Data Release 8. Our results show that the variability sample is the oldest, while the mid-IR sample is the youngest, for which the luminosity at 4020 \AA\ is dominated ($>50\%$) by the young population ($t<10^8$ yr). The light-weighted mean stellar age of the whole sample is in general about 0.7 dex younger than the optical sample studied in Cai et al. We compare the population results between fitting models with and without a power-law (PL) component and find that the neglect of a PL component would lead to an under- and over-estimation by 0.2 and 0.1 dex for the light- and mass-weighted mean stellar age, respectively, for our sample of dwarf galaxies, which has a mean fractional contribution of $\sim$16\% from the AGN. In addition, we obtain further evidence for a possible suppression of star formation in the host galaxy by the central AGN. We also find that there exists an anti-correlation between the extinction-corrected [O\,{\sc iii}] luminosity and light-weighted mean stellar age, confirming our previous finding that there is a physical connection between AGN and star-forming activities in AGN-host dwarfs., Comment: 25 pages, 11 figures, accepted by RAA

Galaxy interactions and mergers can enhance or reduce star formation, but a complete understanding of the involved processes is still lacking. The effect of dwarf galaxy mergers is even less clear than their massive counterpart. We present a study on a dwarf merger remnant in the Virgo cluster, VCC322, which might form a triple system with VCC334 and VCC319. We identify a prominent long and straight tail-like substructure that has a size comparable to its host galaxy VCC322. By comparing the color-color ($g-r$ vs. $r-H$) distribution with simple stellar population models, we infer that the metallicity and stellar age of this tail are $Z_\star \sim 0.02~Z_\odot$ and $t_\star \sim 10$~Gyr, respectively. In VCC319, we find a sign of isophotal twisting. This suggests that VCC319 may be subject to tidal interaction. An analysis of the SDSS optical spectra of VCC322 indicates mass- and light-weighted ages of about 10$^{9.8}$ yr and 10$^{7.5}$ yr, respectively, indicating an ongoing star formation activity. However, the star formation in VCC322 seems suppressed when compared to other star-forming dwarfs of comparable stellar masses. Our finding of shock excitation of optical emission lines indicates that interaction-induced shock may contribute to the heating of cold gas and suppression of star formation., Comment: 12 pages, 7 figures. Accepted for publication in ApJ

We report physical properties of the brightest ($S_{870\,\mu \rm m}=12.4$-$19.2\,$mJy) and not strongly lensed 18 870$\,\mu$m selected dusty star-forming galaxies (DSFGs), also known as submillimeter galaxies (SMGs), in the COSMOS field. This sample is part of an ALMA band$\,$3 spectroscopic survey (AS2COSPEC), and spectroscopic redshifts are measured in 17 of them at $z=2$-$5$. We perform spectral energy distribution analyses and deduce a median total infrared luminosity of $L_{\rm IR}=(1.3\pm0.1)\times10^{13}\,L_{\odot}$, infrared-based star-formation rate of ${\rm SFR}_{\rm IR}=1390\pm150~M_{\odot}\,\rm yr^{-1}$, stellar mass of $M_\ast=(1.4\pm0.6)\times10^{11}\,M_\odot$, dust mass of $M_{\rm dust}=(3.7\pm0.5)\times10^9\,M_\odot$, and molecular gas mass of $M_{\rm gas}= (\alpha_{\rm CO}/0.8)(1.2\pm0.1)\times10^{11}\,M_\odot$, suggesting that they are one of the most massive, ISM-enriched, and actively star-forming systems at $z=2$-$5$. In addition, compared to less massive and less active galaxies at similar epochs, SMGs have comparable gas fractions; however, they have much shorter depletion time, possibly caused by more active dynamical interactions. We determine a median dust emissivity index of $\beta=2.1\pm0.1$ for our sample, and by combining our results with those from other DSFG samples, we find no correlation of $\beta$ with redshift or infrared luminosity, indicating similar dust grain compositions across cosmic time for infrared luminous galaxies. We also find that AS2COSPEC SMGs have one of the highest dust-to-stellar mass ratios, with a median of $0.02\pm0.01$, significantly higher than model predictions, possibly due to too strong of a AGN feedback implemented in the model. Finally, our complete and uniform survey enables us to put constraints on the most massive end of the dust and molecular gas mass functions., Comment: 25 pages, 13 figures, published in ApJ

GW170817 is the unique gravitational-wave (GW) event that is associated to the electromagnetic (EM) counterpart GRB 170817A. NGC 4993 is identified as the host galaxy of GW170817/GRB 170817A. In this paper, we particularly focus on the spatially resolved properties of NGC 4993. We present the photometric results from the comprehensive data analysis of the high spatial-resolution images in the different optical bands. The morphological analysis reveals that NGC 4993 is a typical early-type galaxy without significant remnants of major galaxy merger. The spatially resolved stellar population properties of NGC 4993 suggest that the galaxy center has passive evolution with the outskirt formed by gas accretion. We derive the merging rate of the compact object per galaxy by a co-evolution scenario of supermassive black hole and its host galaxy. If the galaxy formation is at redshift 1.0, the merging rate per galaxy is $3.2\times 10^{-4}$ to $7.7\times 10^{-5}$ within the merging decay time from 1.0 to 5.0 Gyr. The results provide the vital information for the ongoing GW EM counterpart detections. The HST data analysis presented in this paper can be also applied for the Chinese Space Station Telescope (CSST) research in the future., Comment: RAA accepted

NGC 1266 is a lenticular galaxy (S0) hosting an active galactic nucleus (AGN), and known to contain a large amount of shocked gas. We compare the luminosity ratio of mid-\emph{J} CO lines to IR continuum with star-forming galaxies (SFGs), and then model the CO spectral line energy distribution (SLED). We confirm that in the mid- and high-\emph{J} regions ($J_{\rm up}$ = 4--13), the C-type shock ($v_{\rm s}$ = 25 km s$^{-1}$, $n_{\rm H}$ = $5\times10^{4}$ cm$^{-3}$) can reproduce the CO observations well. The galaxy spectral energy distribution (SED) is constructed and modeled by the code {\tt X-CIGALE} and obtains a set of physical parameters including the star formation rate (SFR, 1.17 $\pm$ 0.47 \emph{M$_{\odot}$}yr$^{-1}$). Also, our work provides SFR derivation of [C\,{\sc ii}] from the neutral hydrogen regions only (1.38 $\pm$ 0.14 $M_{\odot}$yr$^{-1}$). Previous studies have illusive conclusions on the AGN or starburst nature of the NGC 1266 nucleus. Our SED model shows that the hidden AGN in the system is intrinsically low-luminosity, consequently the infrared luminosity of the AGN does not reach the expected level. Archival data from \emph{NuSTAR} hard X-ray observations in the 3--79 keV band shows a marginal detection, disfavoring presence of an obscured luminous AGN and implying that a compact starburst is more likely dominant for the NGC 1266 nucleus.

Using the atomic carbon [CI](1$-$0) and [CI](2$-$1) emission maps observed with the $Herschel\ Space\ Observatory$, and CO(1$-$0), HI, infrared and submm maps from literatures, we estimate the [CI]-to-H$_2$ and CO-to-H$_2$ conversion factors of $\alpha_\mathrm{[CI](1-0)}$, $\alpha_\mathrm{[CI](2-1)}$, and $\alpha_\mathrm{CO}$ at a linear resolution $\sim1\,$kpc scale for six nearby galaxies of M 51, M 83, NGC 3627, NGC 4736, NGC 5055, and NGC 6946. This is perhaps the first effort, to our knowledge, in calibrating both [CI]-to-H$_2$ conversion factors across the spiral disks at spatially resolved $\sim1\,$kpc scale though such studies have been discussed globally in galaxies near and far. In order to derive the conversion factors and achieve these calibrations, we adopt three different dust-to-gas ratio (DGR) assumptions which scale approximately with metallicity taken from precursory results. We find that for all DGR assumptions, the $\alpha_\mathrm{[CI](1-0)}$, $\alpha_\mathrm{[CI](2-1)}$, and $\alpha_\mathrm{CO}$ are mostly flat with galactocentric radii, whereas both $\alpha_\mathrm{[CI](2-1)}$ and $\alpha_\mathrm{CO}$ show decrease in the inner regions of galaxies. And the central $\alpha_\mathrm{CO}$ and $\alpha_\mathrm{[CI](2-1)}$ values are on average $\sim 2.2$ and $1.8$ times lower than its galaxy averages. The obtained carbon abundances from different DGR assumptions show flat profiles with galactocentric radii, and the average carbon abundance of the galaxies is comparable to the usually adopted value of $3 \times 10^{-5}$. We find that both metallicity and infrared luminosity correlate moderately with the $\alpha_\mathrm{CO}$ whereas only weakly with either the $\alpha_\mathrm{[CI](1-0)}$ or carbon abundance, and not at all with the $\alpha_\mathrm{[CI](2-1)}$., Comment: 22 pages, 17 figures, 6 tables. Accepted for publication in MNRAS

Based on MaNGA integral field unit (IFU) spectroscopy we search 60 AGN candidates, which have stellar masses $M_{\star}\leqslant5\times10^{9}$$M_{\odot}$ and show AGN ionization signatures in the BPT diagram. For these AGN candidates, we derive the spatially resolved stellar population with the stellar population synthesis code STARLIGHT and measure the gradients of the mean stellar age and metallicity. We find that the gradients of mean stellar age (metallicity) of individual AGN-host dwarfs are diverse in 0-0.5 Re, 0.5-1 Re and 0-1 Re. However, the overall behavior of the mean stellar age (metallicity) profiles tend to be flat, as the median values of the gradients are close to zero. We further study the overall behavior of the mean stellar age (metallicity) by plotting the co-added radial profiles for the AGN sample and compare with a control sample with similar stellar mass. We find that the median values of light-weighted mean stellar ages of AGN sample are as old as 2-3 ~Gyr within 2 Re,which are about 4-7 times older than those of the control sample. Meanwhile, most of the AGN candidates are low-level AGNs, as only eight sources have L[OIII]>$10^{39.5}$~erg~s$^{-1}$. Hence, the AGNs in dwarf galaxies might accelerate the evolution of galaxies by accelerating the consumption of the gas, resulting in an overall quenching of the dwarf galaxies, and the AGNs also become weak due to the lack of gas. The median values of mass-weighted mean stellar age of both samples within 2 $Re$ are similar and as old as about 10~Gyr, indicating that the stellar mass is mainly contributed by old stellar populations.The gradients of co-added mean stellar metallicity for both samples tend to be negative but close to zero, and the similar mean stellar metallicity profiles for both samples indicate that the chemical evolution of the host galaxy is not strongly influenced by the AGN., Comment: 25 pages, 12 figures, accepted by RAA

In this paper we present our studies on the stellar populations and star formation histories (SFHs) for the Reines et al. sample of 136 dwarf galaxies which host active galactic nuclei (AGNs), selected from the Sloan Digital Sky Survey Data Release 8. We derive stellar populations and reconstruct SFHs for these AGN-host dwarfs using the stellar population synthesis code STARLIGHT. Our results suggest that these AGN-host dwarfs have assembled their stellar masses within a narrow period of time with the stellar mass-weighted ages in the range of $10^9-10^{10}$yr, but show a wide diversity of SFHs with the luminosity-weighted stellar ages in the range of $10^7-10^{10}$yr. The old population ($t>10^9$yr) contributes most to the galaxy light for the majority of the sample; the young population ($t<10^8$yr) also appears in significant but widely varying fractions, while the intermediate-age population ($10^8 10^{39}$erg s$^{-1}$, indicating that there is a physical connection between star formation and AGN activities in these dwarf galaxies., Comment: 12 pages, 10 figures. Accepted for publication in ApJ

A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA HI emission-line mapping, optical imaging and numerical simulations of VCC 848, in order to examine the impact of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its HI gas concentrated within the central high-surface-brightness star-forming region, while the remaining HI is entrained in outlying tidal features. Particularly, a well-defined tidal arm reaches N(HI) comparable to the galaxy center but lacks SF. The molecular gas mass inferred from the current SF rate (SFR) dominates over the atomic gas mass in the central ~ 1.5 kpc. VCC 848 is consistent with being a main-sequence star-forming galaxy for its current stellar mass and SFR. The HII region luminosity distribution largely agrees with that of normal dwarf irregulars with similar luminosities, except that the brightest HII region is extraordinarily luminous. Our N-body/hydrodynamical simulations imply that VCC 848 is a merger between a gas-dominated primary progenitor and a gas-bearing star-dominated secondary. The progenitors had their first passage on a near-radial non-coplanar orbit more than 1 Gyr ago. The merger did not build up a core as compact as typical compact dwarfs with centralized starburst, which may be partly ascribed to the star-dominated nature of the secondary, and in a general sense, a negative stellar feedback following intense starbursts triggered at early stages of the merger., Comment: 25 pages, 14 figures, accepted by ApJ

We present the Atacama Large Millimeter/submillimeter Array (ALMA) observation of the Sub-millimeter galaxy (SMG) ID 141 at z=4.24 in the [N II] 205 $\mu$m line (hereafter [N II]) and the underlying continuum at (rest-frame) 197.6 $\mu$m. Benefiting from lensing magnification by a galaxy pair at z=0.595, ID 141 is one of the brightest z$>4$ SMGs. At the angular resolutions of $\sim1.2"$ to $1.5"$ ($1" \sim6.9$ kpc), our observation clearly separates, and moderately resolves the two lensed images in both continuum and line emission at $\rm S/N>5$ . Our continuum-based lensing model implies an averaged amplification factor of $\sim5.8$ and reveals that the de-lensed continuum image has the S\'ersic index $\simeq 0.95$ and the S\'ersic radius of $\sim0.18" (\sim 1.24$ kpc). Furthermore, the reconstructed [N II] velocity field in the source plane is dominated by a rotation component with a maximum velocity of $\sim 300$ km/s at large radii, indicating a dark matter halo mass of $\sim 10^{12}M_{\odot}$. This, together with the reconstructed velocity dispersion field being smooth and modest in value ($<100$ km/s) over much of the outer parts of the galaxy, favours the interpretation of ID 141 being a disk galaxy dynamically supported by rotation. The observed [N II]/CO (7-6) and [N II]/[C II] 158 $\mu$m line luminosity ratios, which are consistent with the corresponding line ratio vs. far-infrared color correlation from local luminous infrared galaxies, imply a de-lensed star formation rate of ($1.8\pm 0.6)\times10^3M_\odot$/yr and provide an independent estimate on the size of the star-forming region $0.7^{+0.3}_{-0.3}$ kpc in radius., Comment: 13 pages, 6 figures, 2 tables. Lensing model code can be found here https://gitlab.com/cxylzlx/tiny_lens

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner $\sim$ 2 kpc circumnuclear region of NGC253, we present HCN $J=4-3$ and HCO$^+ J=4-3$ maps obtained with the James Clerk Maxwell Telescope (JCMT). With the spatially resolved data, we compute the concentration indices $r_{90}/r_{50}$ for the different tracers. HCN and HCO$^+$ 4-3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1-0 and the stellar component. The dense-gas fraction ($f_\text{dense}$, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO$^+$/CO) and the ratio $R_\text{31}$ (CO 3-2/1-0) decline towards larger galactocentric distances, but increase with higher SFR surface density. The radial variation and the large scatter of $f_\text{dense}$ and $R_\text{31}$ imply distinct physical conditions in different regions of the galactic disc. The relationships of $f_\text{dense}$ versus $\Sigma_\text{stellar}$, and SFE$_\text{dense}$ versus $\Sigma_\text{stellar}$ are explored. SFE$_\text{dense}$ increases with higher $\Sigma_\text{stellar}$ in this galaxy, which is inconsistent with previous work that used HCN 1-0 data. This implies that existing stellar components might have different effects on the high-$J$ HCN and HCO$^+$ than their low-$J$ emission. We also find that SFE$_\text{dense}$ seems to be decreasing with higher $f_\text{dense}$, which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars., Comment: accepted to MNRAS

In this paper we present our imaging observations on the CO(7-6) line and its underlying continuum emission of the young submillimeter galaxy LESS 073 at redshift 4.755, using the Atacama Large Millimeter/submillimeter Array (ALMA). At the achieved resolution of $\sim$$1^{\prime\prime}.2\times0^{\prime\prime}.9$ ($8\times6$~kpc$^2$), the CO(7-6) emission is largely unresolved (with a deconvolved size of $1^{\prime\prime}.1(\pm0^{\prime\prime}.5) \times 0^{\prime\prime}.9(\pm0^{\prime\prime}.8)$), and the continuum emission is totally unresolved. The CO(7-6) line emission has an integrated flux of $0.86\pm0.08$~Jy km/s, and a line width of $343\pm40$ km/s. The continuum emission has a flux density of 0.51 mJy. By fitting the observed far-infrared (FIR) spectral energy distribution of LESS 073 with a single-temperature modified blackbody function, we obtained a dust temperature $T_{\rm dust}=57.6\pm3.5$ K, 60-to-100 $\mu$m flux density ratio $f_{60}/f_{100}=0.86\pm0.08$, and total infrared luminosity $L_{\rm IR}=(5.8\pm0.9) \times 10^{12}~L_\odot$. The SED-fit-based $f_{60}/f_{100}$ is consistent with those estimated from various line ratios as advocated by our earlier work, indicating that those proposed line-ratio-based method can be used to practically derive $f_{60}/f_{100}$ for high-$z$ sources. The total molecular gas mass of LESS 073 is $(3.3\pm1.7) \times10^{10}~M_\odot$, and the inferred gas depletion time is about 43 Myr., Comment: 8 pages, 6 figures, accepted for publication in ApJ

We present maps of atomic carbon [CI](1-0) and [CI](2-1) at a linear resolution ~1kpc scale for a sample of one HII, six LINER, three Seyfert and five starburst galaxies observed with Herschel. We compare spatial distributions of two [CI] lines with that of CO(1-0) emission, and find that both [CI] lines distribute similarly to CO(1-0) emission in most galaxies. We present luminosity ratio maps of L'_[CI](1-0)/L'_CO(1-0), L'_[CI](2-1)/L'_CO(1-0), L'_[CI](2-1)/L'_[CI](1-0) (hereafter R_[CI]) and f_70/f_160. L'_[CI](2-1)/L'_CO(1-0), R_[CI] and f_70/f_160 are centrally peaked in starbursts; whereas remain relatively constant in LINERs, indicating that star-forming activity can enhance carbon emission, especially for [CI](2-1). We explore the correlations between the luminosities of CO(1-0) and [CI] lines, and find that L'_CO(1-0) correlates tightly and almost linearly with both L'_[CI](1-0) and L'_[CI](2-1), suggesting that [CI] lines, similar as CO(1-0), can trace total molecular gas in our resolved galaxies on kpc scales. We investigate the dependence of L'_[CI](1-0)/L'_CO(1-0), L'_[CI](2-1)/L'_CO(1-0) and [CI] excitation temperature T_ex on dust temperature T_dust, and find non-correlation, a weak and modest correlation, respectively. The ratio of L'_[CI](1-0)/L'_CO(1-0) stays smooth distribution in most galaxies, indicating that the conversion factor of [CI](1-0) luminosity to H_2 mass (X_[CI](1-0)) changes with CO(1-0) conversion factor (\alpha_CO) proportionally. Under optically thin and LTE assumptions, we derive a galaxy-wide average carbon excitation temperature T_ex ~ 19.7 \pm 0.5K and an average neutral carbon abundance X[CI]/X[H_2] ~2.5 \pm 1.0 * 10^{-5} in our resolved sample, which is comparable to the usually adopted value of 3*10^{-5}, but ~3 times lower than the carbon abundance in local (U)LIRGs. We conclude that the carbon abundance varies in different galaxy types., Comment: 15 pages, 5 figures, accepted for publication in ApJ

We selected an active galactic nuclei (AGN) sample ($0 < z \le 0.35$) from Sloan Digital Sky Survey Data Release 7, and measured the broad- (${\rm H\alpha^{b}/H\beta^{b}}$) and narrow-line Balmer decrements (${\rm H\alpha^{n}/H\beta^{n}}$) of 554 selected AGNs. We found that the distributions of Balmer decrements can be fitted by a Gaussian function and give the best estimates of ${\rm H\alpha^{b}/H\beta^{b}} = 3.16$ with a standard deviation 0.07 dex, and ${\rm H\alpha^{n}/H\beta^{n}} = 4.37$ with a standard deviation 0.10 dex. We inspected the distributions of ${\rm H\alpha^{b}/H\beta^{b}}$ and ${\rm H\alpha^{n}/H\beta^{n}}$ in the Baldwin$-$Phillips$-$Terlevich (BPT) diagram and found that only narrow-line Balmer decrements depend on the physical conditions of the narrow-line region (NLR). We tested the relationship between ${\rm H\alpha^{b}/H\beta^{b}}$ and ${\rm H\alpha^{n}/H\beta^{n}}$, and found that ${\rm H\alpha^{b}/H\beta^{b}}$ does not correlate with ${\rm H\alpha^{n}/H\beta^{n}}$. We investigated the relationship between Balmer decrements and Seyfert sub-type, and found that only broad-line Balmer decrements correlate with Seyfert sub-type, We also examined the dependency of Balmer decrements on AGN properties, and found that Balmer decrements have no correlation with optical luminosity, but show some dependence on accretion rate. These results indicate that the NLR is subject to more reddening by dust than the broad-line region (BLR)., Comment: 10 pages, 9 figures, 1 table, accepted for publication in MNRAS

We present high-resolution (0.17\arcsec $\times$ 0.14\arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the CO\,(6-5) line, and 435\um\ dust continuum emission within a $\sim$9\arcsec $\times$ 9\arcsec\ area centered on the nucleus of the galaxy NGC\,5135. NGC\,5135 is a well-studied luminous infrared galaxy that also harbors a Compton-thick active galactic nucleus (AGN). At the achieved resolution of 48 $\times$ 40\,pc, the CO\,(6-5) and dust emissions are resolved into gas "clumps" along the symmetrical dust lanes associated with the inner stellar bar. The clumps have radii between $\sim$45-180\,pc and CO\,(6-5) line widths of $\sim$60-88\,\kms. The CO\,(6-5) to dust continuum flux ratios vary among the clumps and show an increasing trend with the \FeII/Br-$\gamma$ ratios, which we interpret as evidence for supernova-driven shocked gas providing a significant contribution to the \co65\ emission. The central AGN is undetected in continuum, nor in CO\,(6-5) if its line velocity width is no less than $\sim$\,40\,\kms. We estimate that the AGN contributes at most 1\% of the integrated CO\,(6-5) flux of 512 $\pm$ 24$\,$Jy\kms\ within the ALMA field of view, which in turn accounts for $\sim$32\% of the CO\,(6-5) flux of the whole galaxy., Comment: 21 pages, 12 figures, Accepted for publication in ApJ

The most intensively star-forming galaxies are extremely luminous at far-infrared (FIR) wavelengths, highly obscured at optical and ultraviolet wavelengths, and lie at $z\ge 1-3$. We present a programme of ${\it Herschel}$ FIR spectroscopic observations with the SPIRE FTS and photometric observations with PACS, both on board ${\it Herschel}$, towards a sample of 45 gravitationally lensed, dusty starbursts across $z\sim 1-3.6$. In total, we detected 27 individual lines down to 3-$\sigma$, including nine $[\rm C{\small II}]$ 158-$\mu$m lines with confirmed spectroscopic redshifts, five possible $[\rm C{\small II}]$ lines consistent with their far-infrared photometric redshifts, and in some individual sources a few $[\rm O{\small III}]$ 88-$\mu$m, $[\rm O{\small III}]$ 52-$\mu$m, $[\rm O{\small I}]$ 145-$\mu$m, $[\rm O{\small I}]$ 63-$\mu$m, $[\rm N{\small II}]$ 122-$\mu$m, and OH 119-$\mu$m (in absorption) lines. To derive the typical physical properties of the gas in the sample, we stack all spectra weighted by their intrinsic luminosity and by their 500-$\mu$m flux densities, with the spectra scaled to a common redshift. In the stacked spectra, we detect emission lines of $[\rm C{\small II}]$ 158-$\mu$m, $[\rm N{\small II}]$ 122-$\mu$m, $[\rm O{\small III}]$ 88-$\mu$m, $[\rm O{\small III}]$ 52-$\mu$m, $[\rm O{\small I}]$ 63-$\mu$m, and the absorption doublet of OH at 119-$\mu$m, at high fidelity. We find that the average electron densities traced by the $[\rm N{\small II}]$ and $[\rm O{\small III}]$ lines are higher than the average values in local star-forming galaxies and ULIRGs, using the same tracers. From the $[\rm N{\small II}]/[\rm C{\small II}]$ and $[\rm O{\small I}]/[\rm C{\small II}]$ ratios, we find that the $[\rm C{\small II}]$ emission is likely dominated by the photo-dominated regions (PDR), instead of by ionised gas or large-scale shocks., Comment: 39 pages, 19 figures, Accepted for publication in MNRAS. For extra pptx slides prepared for this work, please see http://www.eso.org/~zzhang/download/FTS_SMG_survey_ZhiyuZhang.pdf

We present the results from our Atacama Large Millimeter/submillimeter Array (ALMA) imaging observations of the CO (7-6), [CI] 370 um (hereafter [CI]) and [NII] 205 um (hereafter [NI]I) lines and their underlying continuum emission of BRI 1335-0417, an infrared bright quasar at z = 4.407. At the achieved resolutions of 1.1" to 1.2" (or 7.5 to 8.2 kpc), the continuum at 205 and 372 um (rest-frame), the CO (7-6), and the [CI] emissions are at best barely resolved whereas the [NII] emission is well resolved with an ALMA beam de-convolved major axis of 1.3" (+/- 0.3") or 9 (+/-2) kpc. As a warm dense gas tracer, the CO (7-6) emission shows a more compact spatial distribution and a significantly higher peak velocity dispersion than the other two lines that probe lower density gas, a picture favoring a merger-triggered star formation (SF) scenario over an orderly rotating SF disk. The CO (7-6) data also indicate a possible QSO-driven gas outflow that reaches a maximum line-of-sight velocity of 500 to 600 km/s. The far-infrared (FIR) dust temperature (T_dust) of 41.5 K from a gray-body fit to the continuum agrees well with the average T_dust inferred from various line luminosity ratios. The resulting L_CO(7-6)/L_FIR luminosity ratio is consistent with that of local luminous infrared galaxies powered predominantly by SF. The CO(7-6) luminosity-inferred SF rate is 5.1 (+/-1.5) x 10^3 M_solar/yr . The system has an effective star-forming region of 1.7 (+1.7/-0.8) kpc in diameter and a molecular gas reservoir of ~5 x 10^{11} M_solar., Comment: 14 pages, 7 figures; accepted for publication in the Astrophysical Journal

Mid-infrared molecular hydrogen (H$_2$) emission is a powerful cooling agent in galaxy mergers and in radio galaxies; it is a potential key tracer of gas evolution and energy dissipation associated with mergers, star formation, and accretion onto supermassive black holes. We detect mid-IR H$_2$ line emission in at least one rotational transition in 91\% of the 214 Luminous Infrared Galaxies (LIRGs) observed with Spitzer as part of the Great Observatories All-sky LIRG Survey (GOALS). We use H$_2$ excitation diagrams to estimate the range of masses and temperatures of warm molecular gas in these galaxies. We find that LIRGs in which the IR emission originates mostly from the Active Galactic Nuclei (AGN) have about 100K higher H$_2$ mass-averaged excitation temperatures than LIRGs in which the IR emission originates mostly from star formation. Between 10 and 15\% of LIRGs have H$_2$ emission lines that are sufficiently broad to be resolved or partially resolved by the high resolution modules of Spitzer's Infrared Spectrograph (IRS). Those sources tend to be mergers and contain AGN. This suggests that a significant fraction of the H$_2$ line emission is powered by AGN activity through X-rays, cosmic rays, and turbulence. We find a statistically significant correlation between the kinetic energy in the H$_2$ gas and the H$_2$ to IR luminosity ratio. The sources with the largest warm gas kinetic energies are mergers. We speculate that mergers increase the production of bulk in-flows leading to observable broad H$_2$ profiles and possibly denser environments., Comment: 31 pages, 12 figures, 7 tables, accepted for publication in the Astrophysical Journal

We present the analysis of the physical properties of the interstellar medium (ISM) in the nearby early-type galaxy NGC 3665, based on the far-infrared (FIR) photometric and spectroscopic data as observed by the Herschel Space Observatory. The fit to the spectral energy distribution reveals a high dust content in the galaxy, with the dust-to-stellar mass ratio of $M_{\rm dust}$/$M_\ast$ $\sim$ 1.1 $\times$ 10$^{-4}$ that is nearly three times larger than the mean value of local S0+S0a galaxies. For the ionized regions (H~\textsc{ii} regions), the electron density (n$_e$) is around 49.5 $\pm$ 11.9 cm$^{-3}$ based on the [N~\textsc{ii}]\,122\,\mum/[N~\textsc{ii}]\,205\,\mum\ ratio. For the photodissociation regions, the heating efficiency is in the range of 1.26 $\times$ 10$^{-3}$ and 1.37 $\times$ 10$^{-3}$ based on the ([C~\textsc{ii}$]+[$O~\textsc{i}]\,63\,\mum)/$L_{\rm TIR}$, which is slightly lower than other local galaxies; the hydrogen nucleus density and the strength of FUV radiation field are n $\sim$ 10$^{4}$ cm$^{-3}$ and G$_0$ $\sim$ 10$^{-0.25}$, respectively. The above results are consistent with the presence of weak AGN and a low level of star-forming activity in NGC 3665. Our results give strong support to the `morphological quenching' scenario, where a compact, massive bulge can stabilize amount of cool gas against star formation., Comment: 31 pages, 6 figures, accepted to ApJ

We present our observations of the optical intra-day variability (IDV) in $\gamma$-ray BL Lac object Mrk 501. The observations were run with the 1.02 m and 2.4 m optical telescopes at Yunnan Observatories from 2005 April to 2012 May. The light curve at the $R$ band on 2010 May 15 passes both variability tests (the $F$ test and the ANOVA test). A flare within the light curve on 2010 May 15 has a magnitude change $\Delta m = 0.03 \pm 0.005_{\rm{stat}} \pm 0.007_{\rm{sys}}$ mag, \textbf{a darkening timescale of $\tau_{\rm{d}}=$ 26.7 minutes}, and an amplitude of IDV $Amp=2.9\% \pm0.7\%$. A decline \textbf{described by 11 consecutive flux measurements} within the flare can be fitted linearly with a Pearson's correlation coefficient $r = 0.945$ at the confidence level of $> 99.99\%$. Under the assumptions that the IDV is tightly connected to the mass of the black hole, \textbf{and that the flare duration, being two times $\tau_{\rm{d}}$, is representative of the minimum characteristic timescale, we can derive upper bounds to the mass of the black hole}. In the case of the Kerr black hole, the timescale of $\Delta t_{\rm{min}}^{\rm{ob}}=$ 0.89 hours gives $M_{\bullet}\la 10^{9.20} M_{\odot}$, which is consistent with measurements reported in the literature. This agreement indicates that the hypothesis about $M_{\bullet}$ and $\Delta t_{\rm{min}}^{\rm{ob}}$ is consistent with the measurements/data., Comment: accepted for publication in ApJ; 7 figures, 2 tables

We present our high-resolution ($0^{\prime\prime}.15\times0^{\prime\prime}.13$, $\sim$34 pc) observations of the CO(6-5) line emission, which probes the warm and dense molecular gas, and the 434 $\mu$m dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO(6-5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circum-nuclear rotating gas disk, with 90% of the rotation speed arising within a radius of $\lesssim150$ pc. At the scale of our spatial resolution, the CO(6-5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of $\sim$10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the Southwest to Northeast spatial gradient of both CO-to-dust continuum ratio and Pa-$\alpha$ equivalent width. Within the nuclear region (radius$\sim$300 pc) and with a resolution of $\sim$34 pc, the CO line flux (dust flux density) detected in our ALMA observations is $180\pm18$ Jy km/s ($71\pm7$ mJy), which account for 22% (2.4%) of the total value measured by Herschel., Comment: Accepted for publication in ApJ

We present the results from Atacama Large Millimeter/submillimeter Array (ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII]) and the underlying continuum of BRI 1202-0725, an interacting galaxy system at $z =$ 4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two Lyman-$\alpha$ emitters (LAEs), all within $\sim$25 kpc of the QSO. We detect the QSO and SMG in both [NII] and continuum. At the $\sim$$1"$ (or 6.6 kpc) resolution, both QSO and SMG are resolved in [NII], with the de-convolved major axes of $\sim$9 and $\sim$14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of $\sim$$0.7"$. The ratio of the [NII] flux to the existing CO (7$-$6) flux is used to constrain the dust temperature ($T_{\rm dust}$) for a more accurate determination of the FIR luminosity $L_{\rm FIR}$. Our best estimated $T_{\rm dust}$ equals $43 (\pm 2)$ K for both galaxies (assuming an emissivity index $\beta = 1.8$). The resulting $L_{\rm CO(7-6)}/L_{\rm FIR}$ ratios are statistically consistent with that of local luminous infrared galaxies, confirming that $L_{\rm CO(7-6)}$ traces the star formation (SF) rate (SFR) in these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of 5.1 $(6.9) \times 10^3 M_{\odot}$ yr$^{-1}$ ($\pm$ 30%) assuming Chabrier initial mass function, takes place within a diameter (at half maximum) of 1.3 (1.5) kpc, and shall consume the existing 5 $(5) \times 10^{11} M_{\odot}$ of molecular gas in 10 $(7) \times 10^7$ years., Comment: 4 pages, 1 table, 4 figures; accepted for publication in the ApJ Letters

We present a statistical study on the [C I]($^{3} \rm P_{1} \rightarrow {\rm ^3 P}_{0}$), [C I] ($^{3} \rm P_{2} \rightarrow {\rm ^3 P}_{1}$) lines (hereafter [C I] (1$-$0) and [C I] (2$-$1), respectively) and the CO (1$-$0) line for a sample of (ultra)luminous infrared galaxies [(U)LIRGs]. We explore the correlations between the luminosities of CO (1$-$0) and [C I] lines, and find that $L'_\mathrm{CO(1-0)}$ correlates almost linearly with both $L'_ \mathrm{[CI](1-0)}$ and $L'_\mathrm{[CI](2-1)}$, suggesting that [C I] lines can trace total molecular gas mass at least for (U)LIRGs. We also investigate the dependence of $L'_\mathrm{[CI](1-0)}$/$L'_\mathrm{CO(1-0)}$, $L'_\mathrm{[CI](2-1)}$/$L'_\mathrm{CO(1-0)}$ and $L'_\mathrm{[CI](2-1)}$/$L'_\mathrm{[CI](1-0)}$ on the far-infrared color of 60-to-100 $\mu$m, and find non-correlation, a weak correlation and a modest correlation, respectively. Under the assumption that these two carbon transitions are optically thin, we further calculate the [C I] line excitation temperatures, atomic carbon masses, and the mean [C I] line flux-to-H$_2$ mass conversion factors for our sample. The resulting $\mathrm{H_2}$ masses using these [C I]-based conversion factors roughly agree with those derived from $L'_\mathrm{CO(1-0)}$ and CO-to-H$_2$ conversion factor., Comment: Accepted for publication in ApJ Letter

We describe a Herschel Space Observatory 194-671 micron spectroscopic survey of a sample of 121 local luminous infrared galaxies and report the fluxes of the CO $J$ to $J$-1 rotational transitions for $4 \leqslant J \leqslant 13$, the [NII] 205 um line, the [CI] lines at 609 and 370 um, as well as additional and usually fainter lines. The CO spectral line energy distributions (SLEDs) presented here are consistent with our earlier work, which was based on a smaller sample, that calls for two distinct molecular gas components in general: (i) a cold component, which emits CO lines primarily at $J \lesssim 4$ and likely represents the same gas phase traced by CO (1-0), and (ii) a warm component, which dominates over the mid-$J$ regime ($4 < J < 10$) and is intimately related to current star formation. We present evidence that the CO line emission associated with an active galactic nucleus is significant only at $J > 10$. The flux ratios of the two [CI] lines imply modest excitation temperatures of 15 to 30 K; the [CI] 370 um line scales more linearly in flux with CO (4-3) than with CO (7-6). These findings suggest that the [CI] emission is predominately associated with the gas component defined in (i) above. Our analysis of the stacked spectra in different far-infrared (FIR) color bins reveals an evolution of the SLED of the rotational transitions of water vapor as a function of the FIR color in a direction consistent with infrared photon pumping., Comment: 244 pages, 23 figures, 7 tables, accepted for publication in the Astrophysical Journal Supplement Series

We present a study of interstellar medium in the host galaxies of 9 QSOs at 0.1$1 IR bright QSOs. One target, W0752+19, shows an additional broad velocity component (~720 km/s), and exceptionally strong [OI]63$\mu$m emission with LOI/LFIR of $10^{-2}$, an order of magnitude higher than that of average value found among local (U)LIRGs. Combining with the analyses of the {\it SDSS} optical spectra, we conclude that the [OI]63$\mu$m emission in these QSOs is unlikely excited by shocks. We infer that the broad [OI]63 micron emission in W0752+19 could arise from the warm and dense ISM in the narrow line region of the central AGN. Another possible explanation is the existence of a dense gas outflow with $n_{\rm H}\sim10^4$\,cm$^{-3}$, where the corresponding broad [CII] emission is suppressed. Based on the far-IR [OI] and [CII] line ratios, we estimate the constraints on the ISM density and UV radiation field intensity of $n_{\rm H} \lesssim 10^{3.3}$ cm$^{-3}$ and $10^310^4$., Comment: Accepted for publication in ApJ

In this paper, we report our high-resolution ($0^{\prime\prime}.20\times0^{\prime\prime}.14$ or $\sim$$70\times49$ pc) observations of the CO(6-5) line emission, which probes warm and dense molecular gas, and the 434 $\mu$m dust continuum in the nuclear region of NGC 7130, obtained with the Atacama Large Millimeter Array (ALMA). The CO line and dust continuum fluxes detected in our ALMA observations are $1230\pm74$ Jy km s$^{-1}$ and $814\pm52$ mJy, respectively, which account for 100% and 51% of their total respective fluxes. We find that the CO(6-5) and dust emissions are generally spatially correlated, but their brightest peaks show an offset of $\sim$70 pc, suggesting that the gas and dust emissions may start decoupling at this physical scale. The brightest peak of the CO(6-5) emission does not spatially correspond to the radio continuum peak, which is likely dominated by an Active Galactic Nucleus (AGN). This, together with our additional quantitative analysis, suggests that the heating contribution of the AGN to the CO(6-5) emission in NGC 7130 is negligible. The CO(6-5) and the extinction-corrected Pa-$\alpha$ maps display striking differences, suggestive of either a breakdown of the correlation between warm dense gas and star formation at linear scales of $<$100 pc or a large uncertainty in our extinction correction to the observed Pa-$\alpha$ image. Over a larger scale of $\sim$2.1\,kpc, the double-lobed structure found in the CO(6-5) emission agrees well with the dust lanes in the optical/near-infrared images., Comment: Accepted for publication in ApJ

In this paper, we present the measurements of the [NII] 205micron line ([NII]205) for a flux-limited sample of 122 (ultra-)luminous infrared galaxies [(U)LIRGs] and 20 additional normal galaxies, obtained with the Herschel Space Observatory. We explore the far-infrared (FIR) color dependence of the [NII]205 (L[NII]205) to the total infrared (LIR) luminosity ratio, and find that L[NII]205/LIR only depends modestly on the 70-to-160 micron flux density ratio (f70/f160) when f70/f160 <~ 0.6, whereas such dependence becomes much steeper for f70/f160> 0.6. We also investigate the relation between L[NII]205 and star formation rate (SFR), and show that L[NII]205 has a nearly linear correlation with SFR, albeit the intercept of such relation varies somewhat with f60/f100, consistent with our previous conclusion that \NIIab\ emission can serve as a SFR indicator with an accuracy of ~0.4 dex, or ~0.2 dex if f60/f100 is known independently. Furthermore, together with the ISO measurements of [NII] 122 micron emission we use a total of ~200 galaxies to derive the local [NII]205 luminosity function (LF) by tying it to the known IR LF with a bivariate method. As a practical application, we also compute the local SFR volume density ($\dot{\rho}_{\rm SFR}$) using the newly derived SFR calibrator and LF. The resulting $\log\,\dot{\rho}_{\rm SFR} = -1.96\pm0.11$ $M_\odot$\,yr$^{-1}$\,Mpc$^{-3}$ agrees well with previous studies. Finally, we determine the electron densities ($n_e$) of the ionized medium for a subsample of 12 (U)LIRGs with both [NII]205 and [NII]122 data, and find that $n_e$ is in the range of ~1-100 cm$^{-3}$, with a median value of 22 cm$^{-3}$, Comment: Accepted for publication in ApJ

We investigated the evolutionary stages and disk properties of 211 Young stellar objects (YSOs) across the Perseus cloud by modeling the broadband optical to mid-infrared (IR) spectral energy distribution (SED). By exploring the relationships among the turnoff wave bands lambda_turnoff (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index alpha_excess at lambda <~ 24 microns, and the disk inner radius R_in (from SED modeling) for YSOs of different evolutionary stages, we found that the median and standard deviation of alpha_excess of YSOs with optically thick disks tend to increase with lambda_turnoff, especially at lambda_turnoff >= 5.8 microns, whereas the median fractional dust luminosities L_dust/L_star tend to decrease with lambda_turnoff. This points to an inside-out disk clearing of small dust grains. Moreover, a positive correlation between alpha_excess and R_in was found at alpha_excess > ~0 and R_in > ~10 $\times$ the dust sublimation radius R_sub, irrespective of lambda_turnoff, L_dust/L_star and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing or has little influence on alpha_excess shortward of 24 microns. About 23% of our YSO disks are classified as transitional disks, which have lambda_turnoff >= 5.8 microns and L_dust/L_star >10^(-3). The transitional disks and full disks occupy distinctly different regions on the L_dust/L_star vs. alpha_excess diagram. Taking L_dust/L_star as an approximate discriminator of disks with (>0.1) and without (<0.1) considerable accretion activity, we found that 65% and 35% of the transitional disks may be consistent with being dominantly cleared by photoevaporation and dynamical interaction respectively. [abridged], Comment: 31 pages, 13 figures, 2 tables. To appear in a special issue of RAA on LAMOST sciences

To better characterize the global star formation (SF) activity in a galaxy, one needs to know not only the star formation rate (SFR) but also the rest-frame, far-infrared (FIR) color (e.g., the 60-to-100 $\mu$m color, $C(60/100)$] of the dust emission. The latter probes the average intensity of the dust heating radiation field and scales statistically with the effective SFR surface density in star-forming galaxies including (ultra-)luminous infrared galaxies [(U)LIRGs]. To this end, we exploit here a new spectroscopic approach involving only two emission lines: CO\,(7$-$6) at 372 $\mu$m and [NII] at 205 $\mu$m. For local (U)LIRGs, the ratios of the CO (7$-$6) luminosity ($L_{\rm CO\,(7-6)}$) to the total infrared luminosity ($L_{\rm IR}$; 8$-$1000 $\mu$m) are fairly tightly distributed (to within $\sim$0.12 dex) and show little dependence on $C(60/100)$. This makes $L_{\rm CO\,(7-6)}$ a good SFR tracer, which is less contaminated by active galactic nuclei (AGN) than $L_{\rm IR}$ and may also be much less sensitive to metallicity than $L_{\rm CO\,(1-0)}$. Furthermore, the logarithmic [NII] 205 $\mu$m to CO (7$-$6) luminosity ratio is fairly steeply (at a slope of $\sim$$-1.4$) correlated with $C(60/100)$, with a modest scatter ($\sim$0.23 dex). This makes it a useful estimator on $C(60/100)$ with an implied uncertainty of $\sim$0.15 [or $\lesssim$4 K in the dust temperature ($T_{\rm dust}$) in the case of a graybody emission with $T_{\rm dust} \gtrsim 30$ K and a dust emissivity index $\beta \ge 1$]. Our locally calibrated SFR and $C(60/100)$ estimators are shown to be consistent with the published data of (U)LIRGs of $z$ up to $\sim$6.5., Comment: 6 pages, 3 figures, 1 table; accepted for publication in the ApJ Letter

We report mapping observations of the $^{12}$CO $J=3-2$, $4-3$, $6-5$, and $7-6$ transitions and the CI 492 GHz transition toward the central 40$''\times$40$''$ region of the Circinus galaxy, using the Atacama Pathfinder EXperiment (APEX) telescope. We also detected $^{13}$CO $J=3-2$ at the central position of Circinus. These observations are to date the highest CO transitions reported in Circinus. With large velocity gradient (LVG) modeling and likelihood analysis we try to obtain density, temperature, and column density of the molecular gas in three regions: the nuclear region ($D< 18''\sim$ 360 pc), the entire central 45$''$ ($D<45''\sim$ 900pc) region, and the star-forming (S-F) ring (18$''

We report HCN J=4-3, HCO+ J=4-3, and CS J=7-6 observations in 20 nearby star-forming galaxies with the Acatama Pathfinder EXperiment 12-m telescope. Combined with 4 HCN, 3 HCO+, and 4 CS detections in literature, we probe the empirical link between the luminosity of molecular gas (L_gas) and that of infrared emission (L_IR), up to the highest gas densities (10^6 - 10^8 cm-3) that have been probed so far. For nearby galaxies with large radii, we measure the IR luminosity within the submm beam-size (14"-18") to match the molecular emission. We find linear slopes for L_CS76-L_IR and L_HCN43-L_IR, and a slightly super-linear slope for L_HCO+43-L_IR. The correlation of L_CS76-L_IR even extends over eight orders of luminosity magnitude down to Galactic dense cores, with a fit of log(L_IR)=1.00(\pm 0.01) \times log(L_CS76) + 4.03(\pm 0.04). Such linear correlations appear to hold for all densities >10^4 cm-3, and indicate that star formation rate is not related to free-fall time scale for dense molecular gas., Comment: 7 pages, 3 figures. Comments and suggestions are welcome. Accepted by ApJL