Search

MACS J0717 is the most massive and extended of the Hubble Frontier Field clusters. It is one of the more difficult clusters to model, and we argue that this is, in part, due to the line-of-sight structure (LoS) at redshifts beyond 2. We show that the grale mass reconstruction based on sources at 3 < $$z$$ s < 4.1 has at least 1013 M⊙ more mass than that based on nearby sources, $$z$$ s < 2.6, and attribute the excess mass to a putative LoS, which is at least 75 arcsec from the cluster centre. Furthermore, the lens-model fitted $$z$$ s 's of the recent Kawamata et al. reconstruction are biased systematically low compared to photometric $$z$$ s 's, and the bias is a function of images' distance from the cluster centre. We argue that these mimic the effect of LoS. We conclude that even in the presence of 100–200 images, lens-model adjusted source redshifts can conceal the presence of LoS, demonstrating the existence of degeneracies between $$z$$ s and (sub)structure. Also, a very good fit to image positions is not a sufficient condition for having a high-fidelity mass map: Kawamata et al. obtain an rms of 0.52 arcsec for 173 images of 60 sources; our Grale reconstruction of the exact same data yields a somewhat different map, but similarly low rms, 0.62 arcsec. In contrast, a grale model that uses reasonable, but fixed $$z$$ s gives a worse rms of 1.28 arcsec for 44 sources with 126 images. Unaccounted for LoS can bias the mass map, affecting the magnification and luminosity function estimates of high redshift sources. [ABSTRACT FROM AUTHOR]

We measure the evolution of sizes for star-forming galaxies as seen in 1.4 GHz continuum radio for z  = 0–3. The measurements are based on combined VLA+MERLIN data of the Hubble Deep Field, and using a uv -stacking algorithm combined with model fitting to estimate the average sizes of galaxies. A sample of ∼1000 star-forming galaxies is selected from optical and near-infrared catalogues, with stellar masses M⊙ ≈ 1010–1011 M⊙ and photometric redshifts 0–3. The median sizes are parametrized for stellar mass M * = 5 × 1010 M⊙ as |$R_{\rm e} = A\times {}(H(z)/H(1.5))^{\alpha _z}$|⁠. We find that the median radio sizes evolve towards larger sizes at later times with α z  = −1.1 ± 0.6, and A (the median size at z ≈ 1.5) is found to be |$0. \!\!^{\prime\prime} 26\pm {}0. \!\!^{\prime\prime} 07$| or 2.3±0.6 kpc. The measured radio sizes are typically a factor of 2 smaller than those measure in the optical, and are also smaller than the typical H α sizes in the literature. This indicates that star formation, as traced by the radio continuum, is typically concentrated towards the centre of galaxies, for the sampled redshift range. Furthermore, the discrepancy of measured sizes from different tracers of star formation, indicates the need for models of size evolution to adopt a multiwavelength approach in the measurement of the sizes star-forming regions. [ABSTRACT FROM AUTHOR]

We perform spatially resolved, pixel-by-pixel Spectral Energy Distribution (SED) fitting on galaxies up to z ~ 2.5 in the Hubble eXtreme Deep Field (XDF). Comparing stellar mass estimates from spatially resolved and spatially unresolved photometry we find that unresolved masses can be systematically underestimated by factors of up to 5. The ratio of the unresolved to resolved mass measurement depends on the galaxy's specific star formation rate (sSFR): at low sSFRs the bias is small, but above sSFR ~ 10-9.5 yr-1 the discrepancy increases rapidly such that galaxies with sSFRs ~ 10-8 yr-1 have unresolved mass estimates of only one-half to one-fifth of the resolved value. This result indicates that stellar masses estimated from spatially unresolved data sets need to be systematically corrected, in some cases by large amounts, and we provide an analytic prescription for applying this correction. We show that correcting stellar mass measurements for this bias changes the normalization and slope of the star-forming main sequence and reduces its intrinsic width; most dramatically, correcting for the mass bias increases the stellar mass density of the Universe at high redshift and can resolve the long-standing discrepancy between the directly measured cosmic SFR density at z ≳ 1 and that inferred from stellar mass densities ('the missing mass problem'). [ABSTRACT FROM AUTHOR]

We report the identification of extended Lyα nebulae at z ≃ 3.3 in the Hubble Ultra Deep Field (HUDF, ≃40 kpc x 80 kpc) and behind the Hubble Frontier Field galaxy cluster MACSJ0416 (≃40 kpc), spatially associated with groups of star-forming galaxies. VLT/MUSE integral field spectroscopy reveals a complex structure with a spatially varying double-peaked Lyα emission. Overall, the spectral profiles of the two Lyα nebulae are remarkably similar, both showing a prominent blue emission, more intense and slightly broader than the red peak. From the first nebula, located in the HUDF, no X-ray emission has been detected, disfavouring the possible presence of active galactic nuclei. Spectroscopic redshifts have been derived for 11 galaxies within 2 arcsec from the nebula and spanning the redshift range 1.037 < z < 5.97. The second nebula, behind MACSJ0416, shows three aligned star-forming galaxies plausibly associated with the emitting gas. In both systems, the associated galaxies reveal possible intense rest-frame-optical nebular emissions lines [O iii] λλ4959, 5007+Hβ with equivalent widths as high as 1500 Å rest frame and star formation rates ranging from a few to tens of solar masses per year. A possible scenario is that of a group of young, star-forming galaxies emitting ionizing radiation that induces Lyα fluorescence, therefore revealing the kinematics of the surrounding gas. Also Lyα powered by star formation and/or cooling radiation may resemble the double-peaked spectral properties and the morphology observed here. If the intense blue emission is associated with inflowing gas, then we may be witnessing an early phase of galaxy or a proto-cluster (or group) formation. [ABSTRACT FROM AUTHOR]

ABSTRACT We present new Giant Metre-wave Radio Telescope (GMRT) observations of Hubble Deep Field (HDF) 130, an inverse-Compton (IC) ghost of a giant radio source that is no longer being powered by jets. We compare the properties of HDF 130 with the new and important constraint of the upper limit of the radio flux density at 240 MHz to an analytic model. We learn what values of physical parameters in the model for the dynamics and evolution of the radio luminosity and X-ray luminosity [due to IC scattering of the cosmic microwave background (CMB)] of a Fanaroff-Riley type II (FR II) source are able to describe a source with features (lobe length, axial ratio, X-ray luminosity, photon index and upper limit of radio luminosity) similar to those of the observations. HDF 130 is found to agree with the interpretation that it is an IC ghost of a powerful double-lobed radio source, and we are observing it at least a few Myr after jet activity (which lasted 5-100 Myr) has ceased. The minimum Lorentz factor of injected particles into the lobes from the hotspot is preferred to be γ∼ 103 for the model to describe the observed quantities well, assuming that the magnetic energy density, electron energy density and lobe pressure at time of injection into the lobe are linked by constant factors according to a minimum energy argument, so that the minimum Lorentz factor is constrained by the lobe pressure. We also apply the model to match the features of 6C 0905+3955, a classical double FR II galaxy thought to have a low-energy cut-off of γ∼ 104 in the hotspot due to a lack of hotspot IC X-ray emission. The models suggest that the low-energy cut-off in the hotspots of 6C 0905+3955 is γ≳ 103, just slightly above the particles required for X-ray emission. [ABSTRACT FROM AUTHOR]

We present a search for galaxies at using the latest Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared data, based on the Lyman-break technique. We search for galaxies which have large colours (the '-drops') on account of the Lyman α forest absorption, and with colours inconsistent with being low-redshift contaminants. We identify 24 candidates at redshift (15 are robust and a further nine more marginal but consistent with being high redshift) over an area of arcmin. Previous searches for -drops with WFC3 have focused only on the Hubble Ultra Deep Field, and our larger survey (involving two other nearby deep fields and a wider area survey) has trebled the number of robust -drop candidates. For the first time, we have sufficient galaxies to fit both and of the UV Schechter luminosity function. There is evidence for evolution in this luminosity function from to , in the sense that there are fewer UV-bright galaxies at , consistent with an evolution mainly in . The candidate galaxies we detect have insufficient ionizing flux to reionize the Universe, and it is probable that galaxies below our detection limit provide a significant UV contribution. The faint-end slope, α, is not well constrained. However, adopting a similar faint-end slope to that determined at () and a Salpeter initial mass function (IMF), then the ionizing photon budget still falls short if , even integrating down to . A steeper faint-end slope or a low-metallicity population (or a top-heavy IMF) might still provide sufficient photons for star-forming galaxies to reionize the Universe, but confirmation of this might have to await the James Webb Space Telescope. [ABSTRACT FROM AUTHOR]

We revise and extend the extreme value statistic, introduced in Gupta et al., to study direction dependence in the high-redshift supernova data, arising either from departures, from the cosmological principle or due to direction-dependent statistical systematics in the data. We introduce a likelihood function that analytically marginalizes over the Hubble constant and use it to extend our previous statistic. We also introduce a new statistic that is sensitive to direction dependence arising from living off-centre inside a large void as well as from previously mentioned reasons for anisotropy. We show that for large data sets, this statistic has a limiting form that can be computed analytically. We apply our statistics to the gold data sets from Riess et al., as in our previous work. Our revision and extension of the previous statistic show that the effect of marginalizing over the Hubble constant instead of using its best-fitting value on our results is only marginal. However, correction of errors in our previous work reduces the level of non-Gaussianity in the 2004 gold data that were found in our earlier work. The revised results for the 2007 gold data show that the data are consistent with isotropy and Gaussianity. Our second statistic confirms these results. [ABSTRACT FROM AUTHOR]

We consider the effects of large structures in the Universe on the Hubble diagram. This problem is treated non-linearly by considering a Swiss Cheese model of the Universe in which underdense voids are represented as negatively curved regions of space–time. Exact expressions for luminosity distances and redshifts are used to investigate the non-linear effects of structure on the magnitudes of astrophysical sources. It is found that the intervening voids we consider, between the observer and source, produce changes in apparent magnitude of less than 0.012. Sources inside voids, however, can be affected considerably at redshifts below . By averaging observable quantities over many randomly generated distributions of voids we find that the presence of these structures has the effect of introducing a dispersion around the mean, which itself can be displaced the background value. Observers in an inhomogeneous universe, who take averages of observables along many different lines of sight, may then introduce systematic biases, and underestimate errors, if these effects are not taken into account. Estimates of the potential size of these effects are made using data from simulated large-scale structure. [ABSTRACT FROM AUTHOR]

We present a simplified dynamical model of the ‘Bullet’ system of two colliding clusters. The model constrains the masses of the system by requiring that the orbits of the main and the subcomponents satisfy the cosmological initial conditions of vanishing physical separation a Hubble time ago. This is also known as the timing argument. The model considers a system embedded in an overdense region. We argue that a relative speed of 4500 km s−1 between the two components is consistent with cosmological conditions if the system is of a total mass of and is embedded in a region of a (mild) overdensity of 10 times the cosmological background density. Combining this with the lensing measurements of the projected mass, the model yields a ratio of 3:1 for the mass of the main relative to that of the subcomponent. The effect of the background weakens as the relative speed between the two components is decreased. For relative speeds lower than ∼3700 km s−1, the timing argument yields masses which are too low to be consistent with lensing. [ABSTRACT FROM AUTHOR]

We use the Hubble Ultra Deep Field to study the galaxy luminosity–size distribution. With a careful analysis of selection effects due to both detection completeness and measurement reliability, we identify bias-free regions in the plane for a series of volume-limited samples. By comparison to a nearby survey also having well-defined selection limits, namely the Millennium Galaxy Catalogue, we present clear evidence for evolution in surface brightness since . Specifically, we demonstrate that the mean, rest-frame B-band for galaxies in a sample spanning 8 mag in luminosity between and −14 mag increases by ∼1.0 mag arcsec−2 from to 0.7. We also highlight the importance of considering surface brightness-dependent measurement biases in addition to incompleteness biases. In particular, the increasing, systematic underestimation of Kron fluxes towards low surface brightnesses may cause diffuse, yet luminous, systems to be mistaken for faint, compact objects. [ABSTRACT FROM AUTHOR]

Using the 100-m Green Bank Telescope, we have conducted a cm-wavelength search for CO line emission towards the high-redshift, far-infrared (FIR) luminous object HDF850.1 over the redshift interval 3.3 ≲ z≲ 5.4. Despite the wealth of existing multiwavelength observations, and the recent identification of a galaxy counterpart in deep K′-band (2.2 μm) imaging, an unambiguous spectroscopic redshift has not yet been obtained for this object. A FIR-to-radio wavelength photometric redshift technique, however, predicts a ∼90 per cent probability that the redshift is in the range, (equivalent to an observed redshifted CO emission line frequency, ), making HDF850.1 a potential occupant of the ‘high-redshift tail’ of submillimetre (submm)-selected galaxies. We have also conducted a search for CO line emission over the narrower redshift range, . Although we do not detect any CO line emission in this object, our limits to the CO line luminosity are in broad agreement with the median value measured in the current sample of high-redshift, submm-selected objects detected in high- J CO line emission, but not sufficient to fully test the validity of the photometric redshift technique. [ABSTRACT FROM AUTHOR]

We present a highly simplified model of the dynamical structure of a disc galaxy where only two parameters fully determine the solution, mass and angular momentum. We show through simple physical scalings that once the mass has been fixed, the angular momentum parameter λ is expected to regulate such critical galactic disc properties as colour, thickness of the disc and bulge-to-disc ratio. It is, hence, expected to be the determinant physical ingredient resulting in a given Hubble type. A simple analytic estimate of λ for an observed system is provided. An explicit comparison of the distribution of several galactic parameters against both Hubble type and λ is performed using observed galaxies. Both such distributions exhibit highly similar characteristics for all galactic properties studied, suggesting λ as a physically motivated classification parameter for disc galaxies. [ABSTRACT FROM AUTHOR]

We present radio, optical and X-ray-detected counterparts to the submillimetre sources found using SCUBA in theHubble Deep FieldNorth region (GOODS-N). A new counterpart identification statistic is developed to identify properties of galaxies detected at other wavelengths that can be used to aid counterpart identification. We discriminate between criteria that can use used to pre-select submillimetre bright objects, and those that identify the counterpart to a known submillimetre object. Optically faint galaxies detected in the deepest 1.4-GHz radio continuum maps are the only effective way of pre-selecting SCUBA galaxies, and radio sources are the best way to identify counterparts to known submillimetre detections. Looking at radio spectral indices, only the steeper sources (indicative of star formation) are detected in the submillimetre range. Although we find several X-ray identifications, we show that deepChandraimages do not contribute to counterpart identifications, as in all cases they are already detected in the more easily obtained VLA radio maps. We also find no evidence for clustering betweenChandraand SCUBA sources in this field. For a known SCUBA position, the reddest source tends to be the correct association, although we can find no cut on colour, magnitude or clustering property that efficiently pre-selects for SCUBA sources. 15-μmISOsources are statistically detected by SCUBA, but the limiting mid-infrared flux is not low enough to provide useful constraints. We present postage stamp strips for each SCUBA detection in separate bands from X-ray to radio bands, providing direct visual evidence that approximately half of the submillimetre sources in this field remain unidentified, despite an abundance of deep multiwavelength data. [ABSTRACT FROM AUTHOR]

We investigate how a different calibration of the Cepheid period–luminosity (PL) relation, taking into account metallicity corrections, affects the absolute magnitude calibration of Type Ia supernovae (SNe Ia) and, in turn, the determination of the Hubble constant . We use SN Ia light curves from the literature and previously unpublished data to establish the relation, and calibrate the zero point by means of nine SNe Ia with Cepheid-measured distances. This relation is then used to establish the Hubble diagram, and in turn to derive . In the attempt to correct for the host-galaxy extinction, we find that the data suggest a value for the total to selective absorption ratio of , which is smaller than the standard value for our own Galaxy of . Depending on the metallicity correction for the Cepheid PL relation, the value of , and SN sample selection criteria, the value of the Hubble constant takes a value in the range 68–74 km s−1 Mpc−1, with associated uncertainties of the order of 10 per cent. Unpublished photometry is also presented for 18 SNe of our sample (1991S, 1991T, 1992A, 1992K, 1993H, 1993L, 1994D, 1994M, 1994ae, 1995D, 1995ac, 1995bd, 1996bo, 1997bp, 1997br, 1999aa, 1999dk, 2000cx). These data are the results of a long-standing effort in supernova monitoring at ESO – La Silla and Asiago observatories. [ABSTRACT FROM AUTHOR]

Presents an analysis of the submillimeter common user bolometer array observation of the Hubble Deep Field. Review of the observing strategy and data acquisition; Discussion of data reduction algorithms; Consideration of source astrometry and flux calibration uncertainties.

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 µm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). We find reliable optical/near-infrared associations for 32 of the 35 sources detected in this field by Oliver et al. (Paper I): eight of them are identified as stars, one is definitely an active galactic nucleus (AGN), a second seems likely to be an AGN too, while the remaining 22 appear to be normal spiral or starburst galaxies. Using model spectral energy distributions (SEDs) of similar galaxies, we compare methods for estimating the star formation rates (SFRs) in these objects, finding that an estimator based on integrated (3-1000 µm) infrared luminosity reproduces the model SFRs best. Applying this estimator to model fits to the SEDs of our 22 spiral and starburst galaxies, we find that they are forming stars at rates of ∼ 1-100M...yr[sup -l], with a median value of ∼40M...yr[sup -1], assuming an Einstein-de Sitter universe with a Hubble constant of 50 km s[sup -1] Mpc[sup -1], and star formation taking place according to a Salpeter initial mass function (IMF) across the mass range 0.1-100M.... We split the redshift range 0.0 ≤ z ≤ 0.6 into two equal-volume bins to compute raw estimates of the star formation rate density, ...[sub *], contributed by these sources, assuming the same cosmology and IMF as above and computing errors based on estimated uncertainties in the SFRs of individual galaxies. We compare these results with other estimates of ...[sub *] made with the same assumptions, showing them to be consistent with the results of Flores et al. from their ISO survey of the CFRS 1415+52 field. However, the relatively small volume of our survey means that our ...[sub *] estimates suffer from a large sampling variance, implying that our results, by themselves, do not place tight constraints on the global mean star formation rate density. [ABSTRACT FROM AUTHOR]

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 µm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). The final map in each band was constructed by the co-addition of four independent rasters, registered using bright sources securely detected in all rasters, with the absolute astrometry being defined by a radio source detected at both 6.7 and 15 µm. We sought detections of bright sources in a circular region of radius 2.5 arcmin at the centre of each map, in a manner that simulations indicated would produce highly reliable and complete source catalogues using simple selection criteria. Merging source lists in the two bands yielded a catalogue of 35 distinct sources, which we calibrated photometrically using photospheric models of late-type stars detected in our data. We present extragalactic source count results in both bands, and discuss the constraints that they impose on models of galaxy evolution, given the volume of space sampled by this galaxy population. [ABSTRACT FROM AUTHOR]

Using the 850-μm SCUBA camera on the JCMT and a scanning technique different from other sub-mm surveys, we have obtained a 125 arcmin[sup 2] map centred on the Hubble Deep Field . The 1σ sensitivity to point sources is roughly 3 mJy and thus our map probes the brighter end of the sub-mm source counts. We find six sources with a flux greater than about 12 mJy (>4σ ) and, after a careful accounting of incompleteness and flux bias, estimate the integrated density of bright sources &formmu0; (68 per cent confidence bounds). [ABSTRACT FROM AUTHOR]

We present an analysis of the evolution of galaxy clustering in the redshift interval in the Hubble Deep Field South (HDF-South). The HST optical data are combined with infrared ISAAC/VLT observations, and photometric redshifts are used for all the galaxies brighter than . The clustering signal is obtained in different redshift bins using two different approaches: a standard one, which uses the best redshift estimate of each object, and a second one, which takes into account the redshift probability function of each object. This second method makes it possible to improve the information in the redshift intervals where contamination from objects with insecure redshifts is important. With both methods, we find that the clustering strength up to in the HDF-South is consistent with the previous results in the HDF-North. Whereas at redshift lower than the HDF galaxy population is un/anti-biased with respect to the underlying dark matter, at high redshift the bias increases up to , depending on the cosmological model. These results support previous claims that, at high redshift, galaxies are preferentially located in massive haloes, as predicted by the biased galaxy formation scenario. In order to quantify the impact of cosmic errors on our analyses, we have used analytical expressions from Bernstein . Once the behaviour of higher-order moments is assumed, our results show that errors in the clustering measurements in the HDF surveys are indeed dominated by pure shot-noise in most regimes, as assumed in our analysis. We also show that future observations with instruments like the Advanced Camera on HST will improve the signal-to-noise ratio by at least a factor of 2, as a consequence, more detailed analyses of the errors will be required. In fact, pure shot-noise will give a smaller contribution with respect to other sources of errors, such as finite volume effects or non-Poissonian discreteness effects. [ABSTRACT FROM AUTHOR]

Focuses on the implication of Hubble Deep Field on the distant edge-darkened radio galaxies. Estimation of the high-redshift space density; Formation of flat-spectrum quasars; Observation of the luminosity functions.

The analysis of the four-colour maps of galaxies in the Hubble Deep Field (HDF) has revealed, in the sample of 0.4

We have extended our previous analysis of morphologically selected elliptical and S0 galaxies in the Hubble Deep Field (HDF) North to include Hubble Space Telescope (HST) data in the HDF South and the HDFS–NICMOS areas. Our final sample amounts to 69 E/S0 galaxies with K<20.15 over an area of 11 arcmin[sup 2]. Although a moderately small number over a modest sky area, this sample benefits from the best imaging and photometric data available on high-redshift galaxies. Multi-waveband photometry allows us to estimate with good accuracy the redshifts for the majority of these galaxies, which lack a spectroscopic measure. We confirm our previous findings that massive E/S0s tend to disappear from flux-limited samples at z>1.4. This adds to the evidence that the rest-frame colours and spectral energy distributions (SEDs) of the numerous objects found at 0.8

We use an 850-μm SCUBA map of the Hubble Deep Field (HDF) to study the dust properties of optically-selected starburst galaxies at high redshift. The optical/infrared (IR) data in the HDF allow a photometric redshift to be estimated for each galaxy, together with an estimate of the visible star-formation rate. The 850-μm flux density of each source provides the complementary information: the amount of hidden, dust-enshrouded star formation activity. Although the 850-μm map does not allow detection of the majority of individual sources, we show that the galaxies with the highest UV star-formation rates are detected statistically, with a flux density of about S[sub 850]=0.2 mJy for an apparent UV star-formation rate of 1 h[sup -2] M[sub ⊙] yr[sup -1]. This level of submillimetre output indicates that the total star-forming activity is on average a factor of approximately 6 times larger than the rate inferred from the UV output of these galaxies. The general population of optical starbursts is then predicted to contribute at least 25 per cent of the 850-μm background. We carry out a power-spectrum analysis of the map, which yields some evidence for angular clustering of the background source population, but at a level lower than that seen in Lyman-break galaxies. Together with other lines of argument, particularly from the NICMOS HDF data, this suggests that the 850-μm background originates over an extremely wide range of redshifts – perhaps 1&lsim;z&lsim;6. [ABSTRACT FROM AUTHOR]

Focuses on the color selection of candidate high-redshift galaxies in Hubble Deep Field South using the Lyman dropout scheme. Comparison of selection technique with existing data Hubble Deep Field North; Presence of lower redshift interlopers in the selection; Discussion of the morphologies and luminosity functions of the high-redshift objects.

We present a correlation function analysis for the catalogue of photometric redshifts obtained from the Hubble Deep Field image by Fernandez-Soto, Lanzetta & Yahil. By dividing the catalogue into redshift bins of width Δz=0.4 we measured the angular correlation function w(θ) as a function of redshift up to z∼4.8. From these measurements we derive the trend of the correlation length r[sub 0]. We find that r[sub 0](z) is roughly constant with look-back time up to z≃2, and then increases to higher values at z&gsim;2.4. We estimate the values of r[sub 0], assuming ξ(r,z)=[rr[sub 0](z)][sup -γ], γ=1.8 and various geometries. For Ω[sub 0]=1 we find r[sub 0](z=3)≃7.00±4.87 h[sup -1] Mpc, in good agreement with the values obtained from analysis of the Lyman break galaxies. [ABSTRACT FROM AUTHOR]

We report the discovery of a variable object in the Hubble Deep Field North (HDF-N) which brightened, during the 8.5 d sampled by the data, by more than 0.9 mag in I[sub 814] and about 0.7 mag in V[sub 606], remaining stable in B[sub 450]. Subsequent observations of the HDF-N show that two years later this object has dimmed to about its original brightness in I[sub 814]. The colours of this object, its brightness, its time behaviour in the various filters and the evolution of its morphology are consistent with it being a Type Ib supernova in a faint galaxy at z. [ABSTRACT FROM AUTHOR]

We compare the results of Grimm, Gilfanov & Sunyaev and Ranalli, Comastri & Seti on the (X-ray luminosity–star formation rate) relation in normal galaxies. Based on the –stellar mass dependence for low-mass X-ray binaries (LMXBs), we show that low-SFR (≲1 M⊙ yr−1) galaxies in the Ranalli et al. sample are contaminated by the X-ray emission from LMXBs, unrelated to the current star formation activity. However, the most important conclusion from our comparison is that, after the data are corrected for the ‘LMXB contamination’, the two data sets become consistent with each other, despite differences in their content, variability effects, adopted source distances, X-ray fluxes and SFR determinations, and also in the cosmological parameters used in interpreting the Hubble Deep Field North (HDF-N) data. They also agree well, both in the low- and high-SFR regimes, with the predicted dependence derived from the parameters of the ‘universal’ high-mass X-ray binary (HMXB) luminosity function. This encouraging result emphasizes the potential of the X-ray luminosity as an independent SFR indicator for normal galaxies. [ABSTRACT FROM AUTHOR]

We present the K-band Hubble diagrams ( K– z relations) of submillimetre-selected galaxies and hyperluminous galaxies (HLIRGs). We report the discovery of a remarkably tight K– z relation of HLIRGs, indistinguishable from that of the most luminous radio galaxies. Like radio galaxies, the HLIRG K– z relation at is consistent with a passively evolving ∼3 L* instantaneous starburst starting from a redshift of . In contrast, many submillimetre-selected galaxies are ≳2 mag fainter, and the population has a much larger dispersion. We argue that dust obscuration and/or a larger mass range may be responsible for this scatter. The galaxies so far proved to be hyperluminous may have been biased towards higher AGN bolometric contributions than submillimetre-selected galaxies due to the 60-μm selection of some, so the location on the K– z relation may be related to the presence of the most massive active galactic nucleus. Alternatively, a particular host galaxy mass range may be responsible for both extreme star formation and the most massive active nuclei. [ABSTRACT FROM AUTHOR]