8 research outputs found
Luminous starbursts in the redshift desert at zā¼ 1-2: Star formation rates, masses and evidence for outflows
We present a spectroscopic catalogue of 40 luminous starburst galaxies at z= 0.7ā1.7 (median z= 1.3). 19 of these are submillimetre galaxies (SMGs) and 21 are submillimetre-faint radio galaxies (SFRGs). This sample helps us to fill in the redshift desert at z= 1.2ā1.7 in previous studies as well as to probe a lower luminosity population of galaxies. Radio fluxes are used to determine star formation rates for our sample which range from around 50ā500 Mā yrā1 and are generally lower than those in zā¼ 2 SMGs. We identify nebular [O ii] 3727 emission in the rest-UV spectra and use the linewidths to show that SMGs and SFRGs in our sample have larger linewidths and therefore dynamical masses than optically selected star-forming galaxies at similar redshifts. The linewidths are indistinguishable from those measured in the zā¼ 2 SMG populations suggesting little evolution in the dynamical masses of the galaxies between redshift 1 and 2. [Ne v] and [Ne iii] emission lines are identified in a subset of the spectra indicating the presence of an active galactic nucleus (AGN). In addition, a host of interstellar absorption lines corresponding to transitions of Mg ii and Fe ii ions are also detected. These features show up prominently in composite spectra and we use these composites to demonstrate that the absorption lines are present at an average blueshift of ā240 Ā± 50 km sā1 relative to the systemic velocities of the galaxies derived from [O ii]. This indicates the presence of large-scale outflowing interstellar gas in these systems. We do not find any evidence for differences in outflow velocities between SMGs and SFRGs of similar infrared luminosities. We find that the outflow velocities of zā¼ 1.3 SMGs and SFRGs are consistent with the Vā SFR0.3 local envelope seen in lower redshift ultraluminous infrared galaxies (ULIRGs). These observations are well explained by a momentum-driven wind model
A Hubble Space Telescope NICMOS and ACS morphological study of z similar to 2 submillimetre galaxies
We present a quantitative morphological analysis using Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer H160-band imaging and Advanced Camera for Surveys I775-band imaging of 25 spectroscopically confirmed submillimetre galaxies (SMGs) which have redshifts between Graphic (Graphic). Our analysis also employs a comparison sample of more typical star-forming galaxies at similar redshifts (such as Lyman-break Galaxies) which have lower far-infrared luminosities. This is the first large-scale study of the morphologies of SMGs in the near-infrared at ā¼ 0.1 arcsec resolution (ā²1 kpc). We find that the half-light radii of the SMGs (rh= 2.3 Ā± 0.3 and 2.8 Ā± 0.4 kpc in the observed I and H bands, respectively) and asymmetries are not statistically distinct from the comparison sample of star-forming galaxies. However, we demonstrate that the SMG morphologies differ more between the rest-frame UV and optical bands than typical star-forming galaxies and interpret this as evidence for structured dust obscuration. We show that the composite observed H-band light profile of SMGs is better fitted with a high Sersic index (nā¼ 2) than with an exponential disc suggesting the stellar structure of SMGs is best described by a spheroid/elliptical galaxy light distribution. We also compare the sizes and stellar masses of SMGs to local and high-redshift populations and find that the SMGs have stellar densities which are comparable to (or slightly larger than) local early-type galaxies and comparable to luminous, red and dense galaxies at zā¼ 1.5 which have been proposed as direct SMG descendants, although the SMG stellar masses and sizes are systematically larger. Overall, our results suggest that the physical processes occurring within the galaxies are too complex to be simply characterized by the rest-frame UV/optical morphologies which appear to be essentially decoupled from all other observables, such as bolometric luminosity, stellar or dynamical mass
A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII and And XIII
We present the first spectroscopic analysis of the faint M31 satellite galaxies, And XI and And XIII, as well as a re-analysis of existing spectroscopic data for two further faint companions, And IX (correcting for an error in earlier geometric modelling that caused a misclassification of member stars in previous work) and And XII. By combining data obtained using the Deep Imaging Multi-Object Spectrograph (DEIMOS) mounted on the Keck II telescope with deep photometry from the Suprime-Cam instrument on Subaru, we have identified the most probable members for each of the satellites based on their radial velocities (precise to several Graphic down to iā¼ 22), distance from the centre of the dwarf spheroidal galaxies (dSphs) and their photometric [Fe/H]. Using both the photometric and spectroscopic data, we have also calculated global properties for the dwarfs, such as systemic velocities, metallicities and half-light radii. We find each dwarf to be very metal poor ([Fe/H]ā¼ā2 both photometrically and spectroscopically, from their stacked spectrum), and as such, they continue to follow the luminosityāmetallicity relationship established with brighter dwarfs. We are unable to resolve dispersion for And XI due to small sample size and low signal-to-noise ratio, but we set a 1Ļ upper limit of Ļv < 4.5 km sā1. For And IX, And XII and And XIII we resolve velocity dispersions of Ļv= 4.5+3.6ā3.4, 2.6+5.1ā2.6 and 9.7+8.9ā4.5 km sā1, though we note that the dispersion for And XIII is based on just three stars. We derive masses within the half-light radii for these galaxies of 6.2+5.3ā5.1Ć 106, 2.4+6.5ā2.4Ć 106 and 1.1+1.4ā0.7Ć 107 Mā, respectively. We discuss each satellite in the context of the Mateo relations for dSphs, and in reference to the universal halo profiles established for Milky Way dwarfs. Both And IX and And XII fall below the universal halo profiles of Walker et al., indicating that they are less massive than would be expected for objects of their half-light radius. When combined with the findings of McConnachie & Irwin, which reveal that the M31 satellites are twice as extended (in terms of both half-light and tidal radii) as their Milky Way counterparts, these results suggest that the satellite population of the Andromeda system could inhabit haloes that with regard to their central densities are significantly different from those of the Milky Way
High-resolution CO and radio imaging of z similar to 2 ULIRGs: extended CO structures and implications for the universal star formation law
We present high spatial resolution (0.4 arcsec, Graphic kpc) Plateau de Bure Interferometer interferometric data on three ultraluminous infrared galaxies (ULIRGs) at Graphic: two submillimetre galaxies (SMGs) and one submillimetre faint star-forming radio galaxy. The three galaxies have been robustly detected in CO rotational transitions, either 12CO (J= 4Graphic3) or 12CO (J= 3Graphic2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of Graphic2) for intermediate-excitation CO emission in Graphic ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3 arcsec) combined Multi-Element Radio-Linked Interferometer Network-Very Large Array observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to those of the CO observations. This āmatched beamā approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a KennicuttāSchmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high-z star-forming galaxies
The SCUBA-2 Cosmology Legacy Survey: The clustering of submillimetre galaxies in the UKIDSS UDS field
Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850āĪ¼m) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes (Mhalo > 1013 Mā) at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift
The SCUBA-2 Cosmology Legacy Survey: the clustering of submillimetre galaxies in the UKIDSS UDS field
Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of SMGs identified in the SCUBA-2 Cosmology Legacy Survey. We use a catalogue of submillimetre (850āĪ¼m) source identifications derived using a combination of radio counterparts and colour/infrared selection to analyse a sample of 610 SMG counterparts in the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Survey (UKIDSS) Ultra Deep Survey (UDS), making this the largest high-redshift sample of these galaxies to date. Using angular cross-correlation techniques, we estimate the halo masses for this large sample of SMGs and compare them with passive and star-forming galaxies selected in the same field. We find that SMGs, on average, occupy high-mass dark matter haloes (Mhalo > 1013 Mā) at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. We also find evidence of downsizing, in which SMG activity shifts to lower mass haloes at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift.ISSN:0035-8711ISSN:1365-296
A direct calibration of thtae IRX-beta relation in Lyman-break Galaxies at z=3-5
We use a sample of 4209 Lyman-break galaxies (LBGs) at z 3, 4, and 5 in the UKIRT
Infrared Deep Sky Survey Ultra Deep Survey field to investigate the relationship between the
observed slope of the stellar continuum emission in the ultraviolet, Ī², and the thermal dust
emission, as quantified via the so-called āinfrared excessā (IRX ā” LIR/LUV). Through a stacking
analysis, we directly measure the 850-Ī¼m flux density of LBGs in our deep (0.9 mJy) James
Clerk Maxwell Telescope SCUBA-2 850-Ī¼m map as well as deep public Herschel/SPIRE
250-, 350-, and 500-Ī¼m imaging. We establish functional forms for the IRXāĪ² relation to
z ā¼ 5, confirming that there is no significant redshift evolution of the relation, and that the
resulting average IRXāĪ² curve is consistent with a Calzetti-like attenuation law. Comparing
our results with recent works in the literature, we confirm that discrepancies in the slope of
the IRXāĪ² relation are driven by biases in the methodology used to determine the ultraviolet
slopes. Consistent results are found when IRXāĪ² is evaluated by stacking in bins of stellar
mass, and we argue that the near-linear IRXāM relationship is a better proxy for correcting
observed ultraviolet luminosities to total star formation rates, provided an accurate handle on
M and also gives clues as to the physical driver of the role of dust-obscured star formation in
high-redshift galaxie
The SCUBA HAlf degree extragalactic survey - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies
Determining an accurate position for a submillimetre (submm) galaxy (SMG) is the crucial step that enables us to move from the basic properties of an SMG sample ā source counts and 2D clustering ā to an assessment of their detailed, multiwavelength properties, their contribution to the history of cosmic star formation and their links with present-day galaxy populations. In this paper, we identify robust radio and/or infrared (IR) counterparts, and hence accurate positions, for over two-thirds of the SCUBA HAlf-Degree Extragalactic Survey (SHADES) Source Catalogue, presenting optical, 24-Ī¼m and radio images of each SMG. Observed trends in identification rate have given no strong rationale for pruning the sample. Uncertainties in submm position are found to be consistent with theoretical expectations, with no evidence for significant additional sources of error. Employing the submm/radio redshift indicator, via a parametrization appropriate for radio-identified SMGs with spectroscopic redshifts, yields a median redshift of 2.8 for the radio-identified subset of SHADES, somewhat higher than the median spectroscopic redshift. We present a diagnostic colourācolour plot, exploiting Spitzer photometry, in which we identify regions commensurate with SMGs at very high redshift. Finally, we find that significantly more SMGs have multiple robust counterparts than would be expected by chance, indicative of physical associations. These multiple systems are most common amongst the brightest SMGs and are typically separated by 2ā6 arcsec, Graphic at zā¼ 2, consistent with early bursts seen in merger simulations