Hubble Deep Field South Research Articles

New criteria for the selection of galaxy close pairs from cosmological simulations: evolution of the major and minor merger fraction in MUSE deep fields

It remains a challenge to assess the merger fraction of galaxies at different cosmic epochs in order to probe the evolution of their mass assembly. Using the ILLUSTRIS cosmological simulation project, we investigate the relation between the separation of galaxies in a pair, both in velocity and projected spatial separation space, and the probability that these interacting galaxies will merge in the future. From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction. We then probe the evolution of the major and minor merger fraction using the latest Multi-Unit Spectroscopic Explorer (MUSE) deep observations over the Hubble Ultra Deep Field, Hubble Deep Field South, COSMOS-Gr30, and Abell 2744 regions. From a parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366 close pairs spread over a large range of redshifts (0.2 < z < 6) and stellar masses (107 − 1011M⊙). Using the stellar mass ratio between the secondary and primary galaxy as a proxy to split the sample into major, minor, and very minor mergers, we found a total of 183 major, 142 minor, and 47 very minor close pairs corresponding to a mass ratio range of 1:1–1:6, 1:6–1:100, and lower than 1:100, respectively. Due to completeness issues, we do not consider the very minor pairs in the analysis. Overall, the major merger fraction increases up to z ≈ 2−3 reaching 25% for pairs where the most massive galaxy has a stellar mass M⋆ ≥ 109.5 M⊙. Beyond this redshift, the fraction decreases down to ∼5% at z ≈ 6. The major merger fraction for lower-mass primary galaxies with M⋆ ≤ 109.5 M⊙ seems to follow a more constant evolutionary trend with redshift. Thanks to the addition of new MUSE fields and new selection criteria, the increased statistics of the pair samples allow us to significantly shorten the error bars compared to our previous analysis. The evolution of the minor merger fraction is roughly constant with cosmic time, with a fraction of 20% at z < 3 and a slow decrease to 8−13% in the redshift range 3 ≤ z ≤ 6.

The MUSE Hubble Ultra Deep Field Survey

Star-forming galaxies have been found to follow a relatively tight relation between stellar mass (M*) and star formation rate (SFR), dubbed the “star formation sequence”. A turnover in the sequence has been observed, where galaxies with M* < 1010 M⊙ follow a steeper relation than their higher mass counterparts, suggesting that the low-mass slope is (nearly) linear. In this paper, we characterise the properties of the low-mass end of the star formation sequence between 7 ≤ log M*[M⊙] ≤ 10.5 at redshift 0.11 < z < 0.91. We use the deepest MUSE observations of the Hubble Ultra Deep Field and the Hubble Deep Field South to construct a sample of 179 star-forming galaxies with high signal-to-noise emission lines. Dust-corrected SFRs are determined from Hβ λ4861 and Hα λ6563. We model the star formation sequence with a Gaussian distribution around a hyperplane between logM*, logSFR, and log(1 + z), to simultaneously constrain the slope, redshift evolution, and intrinsic scatter. We find a sub-linear slope for the low-mass regime where log SFR [M⊙yr−1] = 0.83+0.07−0.06 log M*[M⊙]+1.74+0.66−0.68 log(1 + z), increasing with redshift. We recover an intrinsic scatter in the relation of σintr = 0.44+0.05−0.04, dex, larger than typically found at higher masses. As both hydrodynamical simulations and (semi-)analytical models typically favour a steeper slope in the low-mass regime, our results provide new constraints on the feedback processes which operate preferentially in low-mass halos.

The MUSE Hubble Ultra Deep Field Survey

The C III] λλ1907, 1909 emission doublet has been proposed as an alternative to Lyman-α in redshift confirmations of galaxies at z ≳ 6 since it is not attenuated by the largely neutral intergalactic medium at these redshifts and is believed to be strong in the young, vigorously star-forming galaxies present at these early cosmic times. We present a statistical sample of 17 C III]-emitting galaxies beyond z ~ 1.5 using ~30 h deep VLT/MUSE integral field spectroscopy covering 2 square arcminutes in the Hubble Deep Field South (HDFS) and Ultra Deep Field (UDF), achieving C III] sensitivities of ~ 2 × 10-17 erg s-1 cm-2 in the HDFS and ~ 7 × 10-18 erg s-1 cm-2 in the UDF. The rest-frame equivalent widths range from 2 to 19 Å. These 17 galaxies represent ~3% of the total sample of galaxies found between 1.5 ≲ z ≲ 4. They also show elevated star formation rates, lower dust attenuation, and younger mass-weighted ages than the general population of galaxies at the same redshifts. Combined with deep slitless grism spectroscopy from the HST/WFC3 in the UDF, we can tie the rest-frame ultraviolet C III] emission to rest-frame optical emission lines, namely [O III] λ5007, finding a strong correlation between the two. Down to the flux limits that we observe (~ 1 × 10-18 erg s-1 cm-2 with the grism data in the UDF), all objects with a rest-frame [O III] λλ4959, 5007 equivalent width in excess of 250 Å, the so-called extreme emission line galaxies, have detections of C III] in our MUSE data. More detailed studies of the C III]-emitting population at these intermediate redshifts will be crucial to understand the physical conditions in galaxies at early cosmic times and to determine the utility of C III] as a redshift tracer.

The MUSE Hubble Ultra Deep Field Survey

We present spatially resolved stellar kinematic maps, for the first time, for a sample of 17 intermediate redshift galaxies (0.2 < z < 0.8). We used deep MUSE/VLT integral field spectroscopic observations in the Hubble Deep Field South (HDFS) and Hubble Ultra Deep Field (HUDF), resulting from ~30h integration time per field, each covering 1'x1' field of view, with ~0.65" spatial resolution. We selected all galaxies brighter than 25mag in the I band and for which the stellar continuum is detected over an area that is at least two times larger than the spatial resolution. The resulting sample contains mostly late-type disk, main-sequence star-forming galaxies with 10^8.5 - 10^10.5 Msun. Using a full-spectrum fitting technique, we derive two-dimensional maps of the stellar and gas kinematics, including the radial velocity V and velocity dispersion sigma. We find that most galaxies in the sample are consistent with having rotating stellar disks with roughly constant velocity dispersions and that the Vrms=sqrt{V^2+sigma^2} of the gas and stars, a scaling proxy for the galaxy gravitational potential, compare well to each other. These spatially resolved observations of intermediate redshift galaxies suggest that the regular stellar kinematics of disk galaxies that is observed in the local Universe was already in place 4 - 7 Gyr ago and that their gas kinematics traces the gravitational potential of the galaxy, thus is not dominated by shocks and turbulent motions. Finally, we build dynamical axisymmetric Jeans models constrained by the derived stellar kinematics for two specific galaxies and derive their dynamical masses. These are in good agreement (within 25%) with those derived from simple exponential disk models based on the gas kinematics. The obtained mass-to-light ratios hint towards dark matter dominated systems within a few effective radii.

Galactic winds with MUSE: A direct detection of Fe ii* emission from a z = 1.29 galaxy

Emission signatures from galactic winds provide an opportunity to directly map the outflowing gas, but this is traditionally challenging because of the low surface brightness. Using very deep observations (27 h) of the Hubble Deep Field South with the Multi Unit Spectroscopic Explorer (MUSE) instrument, we identify signatures of an outflow in both emission and absorption from a spatially resolved galaxy at z = 1.29 with a stellar mass M⋆ = 8 × 109M⊙, star formation rate SFR = 77+40-25 M⊙ yr-1, and star formation rate surface brightness ΣSFR = 1.6M⊙ kpc-2 within the [Oii] λλ3727,3729 half-light radius R1/2, [OII] = 2.76 ± 0.17 kpc. From a component of the strong resonant Mg ii and Fe ii absorptions at −350 km s-1, we infer a mass outflow rate that is comparable to the star formation rate. We detect non-resonant Fe ii* emission, at λ2365, λ2396, λ2612, and λ2626, at 1.2−2.4−1.5−2.7 × 10-18 erg s-1 cm-2 respectively. The flux ratios are consistent with the expectations for optically thick gas. By combining the four non-resonant Fe ii* emission lines, we spatially map the Fe ii* emission from an individual galaxy for the first time. The Fe ii* emission has an elliptical morphology that is roughly aligned with the galaxy minor kinematic axis, and its integrated half-light radius, R1/2, Fe ii ∗ =4.1 ± 0.4 kpc, is 70% larger than the stellar continuum (R1/2,⋆ ≃2.34 ± 0.17) or the [Oii] nebular line. Moreover, the Fe ii* emission shows a blue wing extending up to −400 km s-1, which is more pronounced along the galaxy minor kinematic axis and reveals a C-shaped pattern in a p−v diagram along that axis. These features are consistent with a bi-conical outflow.

MUSE deep-fields: the Ly α luminosity function in the Hubble Deep Field-South at 2.91 &lt; z &lt; 6.64

We present the first estimate of the Ly{\alpha} luminosity function using blind spectroscopy from the Multi Unit Spectroscopic Explorer, MUSE, in the Hubble Deep Field South. Using automatic source-detection software, we assemble a homogeneously-detected sample of 59 Ly{\alpha} emitters covering a flux range of -18.0 < log10 (F) < -16.3 (erg s^-1 cm^-2), corresponding to luminosities of 41.4 < log10 (L) < 42.8 (erg s^-1). As recent studies have shown, Ly{\alpha} fluxes can be underestimated by a factor of two or more via traditional methods, and so we undertake a careful assessment of each object's Ly{\alpha} flux using a curve-of-growth analysis to account for extended emission. We describe our self-consistent method for determining the completeness of the sample, and present an estimate of the global Ly{\alpha} luminosity function between redshifts 2.91 < z < 6.64 using the 1/Vmax estimator. We find the luminosity function is higher than many number densities reported in the literature by a factor of 2 - 3, although our result is consistent at the 1{\sigma} level with most of these studies. Our observed luminosity function is also in good agreement with predictions from semi-analytic models, and shows no evidence for strong evolution between the high- and low-redshift halves of the data. We demonstrate that one's approach to Ly{\alpha} flux estimation does alter the observed luminosity function, and caution that accurate flux assessments will be crucial in measurements of the faint end slope. This is a pilot study for the Ly{\alpha} luminosity function in the MUSE deep-fields, to be built on with data from the Hubble Ultra Deep Field which will increase the size of our sample by almost a factor of 10.

Deep MUSE observations in the HDFS

(Abridged) We make use of the deepest VLT/MUSE observations performed so far on the Hubble Deep Field South (HDFS) to characterize the low-mass (< $10^{10}$M$_\odot$) galaxy population at intermediate redshift. We identify a sample of 28 spatially-resolved emission-line galaxies in the deep (27h integration time) MUSE data cube, spread over a redshift interval of 0.2 < z < 1.4. The public HST images and multi-band photometry over the HDFS are used to constrain the stellar mass and star formation rate (SFR) of the galaxies and to perform a morphological analysis. We derive the resolved ionized gas properties of these galaxies from the MUSE data and model the disk (both in 2D and with GalPaK$^{\rm 3D}$) to retrieve their intrinsic gas kinematics. We build a sample of resolved emission-line galaxies of much lower stellar mass and SFR (by $\sim$1-2 orders of magnitude) than previous 3D spectroscopic surveys. Most of the spatially-resolved MUSE-HDFS galaxies have gas kinematics consistent with disk-like rotation, but about 20% have velocity dispersions larger than the rotation velocities, and 30% are part of a close pair and/or show clear signs of recent gravitational interactions. In the high-mass regime, the MUSE-HDFS galaxies follow the Tully-Fisher relation defined from previous surveys in a similar redshift range. This scaling relation extends also to lower masses/velocities but with a higher dispersion. The MUSE-HDFS galaxies follow the scaling relations defined in the local universe between the specific angular momentum and the stellar mass. However, we find that intermediate-redshift star-forming galaxies fill a continuum transition from the spiral to elliptical local scaling relations, according to the dynamical state of the gas. This indicates that some galaxies may lose their angular momentum and become dispersion-dominated prior to becoming passive.

SELFI: an object-based, Bayesian method for faint emission line source detection in MUSE deep field data cubes

We present SELFI, the Source Emission Line FInder, a new Bayesian method optimized for detection of faint galaxies in Multi Unit Spectroscopic Explorer (MUSE) deep fields. MUSE is the new panoramic integral field spectrograph at the Very Large Telescope (VLT) that has unique capabilities for spectroscopic investigation of the deep sky. It has provided data cubes with 324 million voxels over a single 1 arcmin2 field of view. To address the challenge of faint-galaxy detection in these large data cubes, we developed a new method that processes 3D data either for modeling or for estimation and extraction of source configurations. This object-based approach yields a natural sparse representation of the sources in massive data fields, such as MUSE data cubes. In the Bayesian framework, the parameters that describe the observed sources are considered random variables. The Bayesian model leads to a general and robust algorithm where the parameters are estimated in a fully data-driven way. This detection algorithm was applied to the MUSE observation of Hubble Deep Field-South. With 27 h total integration time, these observations provide a catalog of 189 sources of various categories and with secured redshift. The algorithm retrieved 91% of the galaxies with only 9% false detection. This method also allowed the discovery of three new Lyα emitters and one [OII] emitter, all without any Hubble Space Telescope counterpart. We analyzed the reasons for failure for some targets, and found that the most important limitation of the method is when faint sources are located in the vicinity of bright spatially resolved galaxies that cannot be approximated by the Sersic elliptical profile.

Extended Lymanαhaloes around individual high-redshift galaxies revealed by MUSE

We report the detection of extended Ly alpha emission around individual star-forming galaxies at redshifts z = 3-6 in an ultradeep exposure of the Hubble Deep Field South obtained with MUSE on the ESO-VLT. The data reach a limiting surface brightness (1sigma) of ~1 x 10^-19 erg s^-1 cm^-2 arcsec^-2 in azimuthally averaged radial profiles, an order of magnitude improvement over previous narrowband imaging. Our sample consists of 26 spectroscopically confirmed Ly alpha-emitting, but mostly continuum-faint (m_AB >~ 27) galaxies. In most objects the Ly alpha emission is considerably more extended than the UV continuum light. While 5 of the faintest galaxies in the sample show no significantly detected Ly alpha haloes, the derived upper limits suggest that this is just due to insufficient S/N. Ly alpha haloes therefore appear to be (nearly) ubiquitous even for low-mass (~10^8-10^9 M_sun) star-forming galaxies at z>3. We decompose the Ly alpha emission of each object into a compact `continuum-like' and an extended halo component, and infer sizes and luminosities of the haloes. The extended Ly alpha emission approximately follows an exponential surface brightness distribution with a scale length of a few kpc. While these haloes are thus quite modest in terms of their absolute sizes, they are larger by a factor of 5-15 than the corresponding rest-frame UV continuum sources as seen by HST. They are also much more extended, by a factor ~5, than Ly alpha haloes around low-redshift star-forming galaxies. Between ~40% and >90% of the observed Ly alpha flux comes from the extended halo component, with no obvious correlation of this fraction with either the absolute or the relative size of the Ly alpha halo. Our observations provide direct insights into the spatial distribution of at least partly neutral gas residing in the circumgalactic medium of low to intermediate mass galaxies at z > 3.

A MUSE View of the HDFS: The Lyα Luminosity Function out to z~6

AbstractWe present preliminary results from MUSE on the Lyα luminosity function in the Hubble Deep Field South (HDFS). Using a large homogeneous sample of LAEs selected through blind spectroscopy, we utilise the unprecedented detection power of MUSE to study the progenitors of L* galaxies back to when the Universe was just ~2 Gyr old. We present these results in the context of the current literature, and highlight the importance of the forthcoming Hubble Ultra Deep Field (HUDF) study with MUSE, which will increase the size of our sample by a factor of ~ 10.

The MUSE 3D view of theHubbleDeep Field South

We observed the Hubble Deep Field South with the new panoramic integral field spectrograph MUSE that we built and just commissioned at the VLT. The data cube resulting from 27 hours of integration covers one arcmin^2 field of view at an unprecedented depth with a 1 sigma emission line surface brightness limit of 1x$10^{-19}$ erg/s/cm$^2$/arcsec$^2$ and contains ~90,000 spectra. We present the combined and calibrated data cube, and we perform a first-pass analysis of the sources detected in the HDF-S imaging. We measured the redshifts of 189 sources up to a magnitude F814W = 29.5, increasing by more than an order of magnitude the number of known spectroscopic redshifts in this field. We also discovered 26 Lya emitting galaxies which are not detected in the HST WFPC2 deep broad band images. The intermediate spectral resolution of 2.3{\AA} allows us to separate resolved asymmetric Lya emitters, [O II] emitters, and C III] emitters and the large instantaneous wavelength range of 4500{\AA} helps to identify single emission lines. We also show how the three dimensional information of MUSE helps to resolve sources which are confused at ground-based image quality. Overall, secure identifications are provided for 83% of the 227 emission line sources detected in the MUSE data cube and for 32% of the 586 sources identified in the HST catalog of Casertano et al 2000. The overall redshift distribution is fairly flat to z=6.3, with a reduction between z=1.5 to 2.9, in the well-known redshift desert. The field of view of MUSE also allowed us to detect 17 groups within the field. We checked that the number counts of [O II] and Ly-a emitters are roughly consistent with predictions from the literature. Using two examples we demonstrate that MUSE is able to provide exquisite spatially resolved spectroscopic information on intermediate redshift galaxies present in the field.

MIPS 24 μm OBSERVATIONS OF THE HUBBLE DEEP FIELD SOUTH: PROBING THE IR-RADIO CORRELATION OF GALAXIES ATz&gt;1

We present MIPS 24 micron observations of the Hubble Deep Field South taken with the Spitzer Space Telescope. The resulting image is 254 arcmin^2 in size and has a sensitivity ranging between ~12 to ~30 microJy rms, with a median sensitivity of ~20 microJy rms. A total of 495 sources have been cataloged with a signal-to-noise ratio greater than 5 sigma. The source catalog is presented as well as source counts which have been corrected for completeness and flux boosting. The IR sources are then combined with MUSYC optical/NIR and ATHDFS radio observations to obtain redshifts and radio flux densities of the sample. We use the IR/radio flux density ratio (q_24) to explore the IR-radio correlation for this IR sample and find q_24 = 0.71 +- 0.31 for sources detected in both IR and radio. The results are extended by stacking IR sources not detected in the radio observations and we derive an average q_24 for redshift bins between 0 < z < 2.5. We find the high redshift (z > 1) sources have an average q_{24} ratio which is better fit by local LIRG SEDs rather than local ULIRG SEDs, indicating that high redshift ULIRGs differ in their IR/radio properties. So ULIRGs at high redshift have SEDs different from those found locally. Infrared faint radio sources are examined, and while nine radio sources do not have a MIPS detection and are therefore radio-loud AGN, only one radio source has an extreme IRAC 3.6 micron to radio flux density ratio indicating it is a radio-loud AGN at z > 1.

Clustering and descendants of MUSYC galaxies at z &lt; 1.5

We measure the evolution of galaxy clustering out to a redshift of z~1.5 using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S) and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift information to calculate the projected-angular correlation function, omega(sigma), from which we infer the projected correlation function Xi(sigma). We demonstrate that this technique delivers accurate measurements of clustering even when large redshift measurement errors affect the data. To this aim we use two mock MUSYC fields extracted from a LambdaCDM simulation populated with GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy of our estimates of Xi(sigma) and to identify and correct for systematic effects in our measurements. We study the evolution of clustering for volume limited subsamples of galaxies selected using their photometric redshifts and rest-frame r-band absolute magnitudes. We find that the real-space correlation length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered out to z~1.5, particularly for ECDF-S given its near-infrared photometric coverage. There is mild evidence for a luminosity dependent clustering in both fields at the low redshift samples (up to <z>=0.57), where the correlation length is higher for brighter galaxies by up to 1Mpc/h between median rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the photometric redshift measurement, each galaxy is assigned a best-fit template; we restrict to E and E+20%Sbc types to construct subsamples of early type galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift increases, making it unlikely (95% level) that ETGs at median redshift z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent passively evolved luminosities. (ABRIDGED)

OPTICAL SPECTROSCOPY OF DISTANT RED GALAXIES

We present optical spectroscopic follow-up of a sample of Distant Red Galaxies (DRGs) with K < 22.5 (Vega), selected by J-K > 2.3, in the Hubble Deep Field South, the MS 1054-03 field, and the Chandra Deep Field South. Spectroscopic redshifts were obtained for 15 DRGs. Only 2 out of 15 DRGs are located at z < 2, suggesting a high efficiency to select high-redshift sources. From other spectroscopic surveys in the CDFS targeting intermediate to high redshift populations selected with different criteria, we find spectroscopic redshifts for a further 30 DRGs. We use the sample of spectroscopically confirmed DRGs to establish the high quality (scatter in \Delta z/(1+z) of ~ 0.05) of their photometric redshifts in the considered deep fields, as derived with EAZY (Brammer et al. 2008). Combining the spectroscopic and photometric redshifts, we find that 74% of DRGs with K < 22.5 lie at z > 2. The combined spectroscopic and photometric sample is used to analyze the distinct intrinsic and observed properties of DRGs at z < 2 and z > 2. In our photometric sample to K < 22.5, low-redshift DRGs are brighter in K than high-redshift DRGs by 0.7 mag, and more extincted by 1.2 mag in Av. Our analysis shows that the DRG criterion selects galaxies with different properties at different redshifts. Such biases can be largely avoided by selecting galaxies based on their rest-frame properties, which requires very good multi-band photometry and high quality photometric redshifts.

Dynamical properties of a large young disk galaxy atz= 2.03

Context. The study of high redshift Tully-Fisher relations (TFRs) is limited by the use of long slit spectrographs, rest frame B band and star formation selected galaxies. Aims. We try to circumvent these issues by using integral field spectroscopy (SINFONI), by studying the rest frame K band and stellar mass TFR, and by selecting targets without a bias to strongly star forming galaxies. In this paper, we demonstrate our methods on our best case. This galaxy, F257, at $z=2.03$, was selecte from a sample of candidate high redshift large disk galaxies in the Hubble Deep Field South that were selected with photometric and morphological criteria. Methods. We used SINFONI at the VLT to obtain an integral field spectrum of the H α line and hence a velocity field and rotation curve. We also use UBVIJHK +IRAC band photometry to determine a stellar photometric mass. Results. We find that F257 is indistinguishable from local late type galaxies in many respects: it has a regular velocity field, increasing velocity disperion towards its center, its rotation curve flattens at 1-2 disk scale lengths, it has the same specific angular momentum as local disks, its properties are consistent with the local K band TFR. Although mainly rotationally supported, its gas component is dynamically heated with respect to local galaxies ($V/\sigma_{z}\sim4$) and it is offset from the local stellar mass TFR at the $2\sigma$ level. But, this offset depends on the SED modeling parameters. In particular, for a 2-component star formation history (SFH), F257 is in agreement with the local stellar mass TFR. F257 is then a nearly (~$75\%$) maximum disk. The dynamical properties of F257 are more like those of local galaxies than those of any other galaxy at similar redshift observed to date. However, the gas-to-stellar mass ratio is unusally large: 2.5.

RADIO OBSERVATIONS OF THE HUBBLE DEEP FIELD-SOUTH REGION. IV. OPTICAL PROPERTIES OF THE FAINT RADIO POPULATION

The Australia Telescope Hubble Deep Field-South (ATHDFS) survey of the Hubble Deep Field South reaches sensitivities of ~10 miceoJyJy at 1.4, 2.5, 5.2 and 8.7 GHz, making the ATHDFS one of the deepest surveys ever performed with the Australia Telescope Compact Array. Here we present the optical identifications of the ATHDFS radio sources using data from the literature. We find that ~66% of the radio sources have optical counterparts to I = 23.5 mag. Deep HST imaging of the area identifies a further 12% of radio sources. We present new spectroscopic observations for 98 of the radio sources, and supplement these spectroscopic redshifts with photometric ones calculated from 5-band optical imaging. The host galaxy colors and radio-to-optical ratios indicate that low luminosity (or "radio quiet") AGN make up a significant proportion of the sub-mJy radio population, a result which is in accordance with a number of other deep radio studies. The radio-to-optical ratios of the bright (S_1.4GHz > 1 mJy) sources is consistent with a bimodal distribution.

Low Surface Brightness Galaxies Around the Hubble Deep Field South

AbstractWe present results from a study of the SFH of a sample of LSB galaxies around the HDF-S. For the selection of the LSB galaxy candidates we used color–color diagrams, from which we selected the candidates based on their different location in comparison to the HSB galaxy redshift tracks. We compared measured spectra to synthetic SEDs from synthesis evolution models. We were able to fit SEDs in the range of 2 to 5 Gyr to the spectra of the LSB galaxies, while applying the same method to a sample of HSB galaxies resulted in an averaged stellar population of about 10 to 14 Gyr. Therefore, LSB galaxies tend to show much younger averaged stellar populations. This implies that the major star formation event of LSB galaxies took place at a redshift of z ~ 0.2 to 0.4 while for HSB galaxies this tends to be at z ~ 2 to 4.

Radio Observations of the Hubble Deep Field-South Region. III. The 2.5, 5.2, and 8.7 GHz Catalogs and Radio Source Properties

Deep radio observations of a wide region centered on the Hubble Deep Field-South have been performed, providing one of the most sensitive sets of radio observations acquired on the Australia Telescope Compact Array to date. A central rms of ~10 μJy is reached at four frequencies (1.4, 2.5, 5.2, and 8.7 GHz). In this paper the full source catalogs from the 2.5, 5.2, and 8.7 GHz observations are presented to complement Paper II in this series, along with a detailed analysis of image quality and noise. We produce a consolidated catalog by matching sources across all four frequencies of our survey. Radio spectral indices are used to investigate the nature of the radio sources and identify a number of sources with flat or inverted radio spectra, which indicate active galactic nucleus activity. We also find several other interesting sources, including a broad-line-emitting radio galaxy, a giant radio galaxy, and three gigahertz-peaked spectrum sources.

NICMOS Imaging of DRGs in the HDF‐S: A Relation between Star Formation and Size atz∼ 2.5

We present deep, high angular-resolution HST NICMOS imaging in the Hubble Deep Field South (HDF-S), focusing on a subset of 14 distant red galaxies (DRGs) at z ~ 2.5 that have been preselected to have J - K > 2.3. We find a clear trend between the rest-frame optical sizes of these sources and their luminosity-weighted stellar ages as inferred from their broadband spectral energy distributions (SEDs). Galaxies whose SEDs are consistent with being dusty and actively star-forming generally show extended morphologies in the NICMOS images (re ≳ 2 kpc), while the five sources that are not vigorously forming stars are extremely compact (re ≲ 1 kpc). This trend suggests a direct link between the mean ages of the stars and the size and density of the galaxies and supports the conjecture that early events quench star formation and leave compact remnants. Furthermore, the compact galaxies have stellar surface mass densities that exceed those of local galaxies by more than an order of magnitude. The existence of such massive dense galaxies presents a problem for models of early-type galaxy formation and evolution. Larger samples of DRGs and higher spatial resolution imaging will allow us to determine the universality of the results presented here for a small sample.

The Size Evolution of Galaxies sincez∼3: Combining SDSS, GEMS, and FIRES

We present the evolution of the luminosity-size and stellar mass-size relations of luminous (L_V>3.4x10^10h_70^-2L_sun) and of massive (M_*>3x10^10h_70^-2M_sun) galaxies in the last ~11 Gyr. We use very deep near-infrared images of the Hubble Deep Field-South and the MS1054-03 field in the J_s, H and K_s bands from FIRES to retrieve the sizes in the optical rest-frame for galaxies with z>1. We combine our results with those from GEMS at 0.2<z<1 and SDSS at z~0.1 to achieve a comprehensive picture of the optical rest-frame size evolution from z=0 to z=3. Galaxies are differentiated according to their light concentration using the Sersic index n. For less concentrated objects, the galaxies at a given luminosity were typically ~3+-0.5 (+-2 sigma) times smaller at z~2.5 than those we see today. The stellar mass-size relation has evolved less: the mean size at a given stellar mass was \~2+-0.5 times smaller at z~2.5, evolving proportional to (1+z)^{-0.40+-0.06}. Simple scaling relations between dark matter halos and baryons in a hierarchical cosmogony predict a stronger (although consistent within the error bars) than observed evolution of the stellar mass-size relation. The observed luminosity-size evolution out to z~2.5 matches well recent infall model predictions for Milky-Way type objects. For low-n galaxies, the evolution of the stellar mass-size relation would follow naturally if the individual galaxies grow inside-out. For highly concentrated objects, the situation is as follows: at a given luminosity, these galaxies were ~2.7+-1.1 times smaller at z~2.5 (or put differently, were typically ~2.2+-0.7 mag brighter at a given size than they are today), and at a given stellar mass the size has evolved proportional to (1+z)^{-0.45+-0.10}.