Surface Density Of Galaxies Research Articles

The properties of the interstellar medium within a star-forming galaxy at z= 2.3

We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and sub-millimetre, from the lensed z=2.3 sub-millimetre galaxy SMM J2135-0102. We obtain very high signal-to-noise detections of 11 transitions from 3 species and limits on a further 20 transitions from 9 species. We use the 12CO, [CI] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry, and find strong evidence for a two-phase medium comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing photo-dissociation region models we show that on average the molecular gas is exposed to a UV radiation field that is ~1000 x more intense than the Milky Way, with star-forming regions having a characteristic density of n~10^4 /cm^3. These conditions are similar to those found in local ULIRGs and in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic ray flux within clouds. We show that, when integrated over the galaxy, the gas and star-formation surface densities appear to follow the Kennicutt-Schmidt relation, although when compared to high-resolution sub-mm imaging, our data suggest that this relation breaks down on scales of <100pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z~2.3 at a level of detail that has only recently become possible at z<0.1, and show the potential physical properties that will be studied in unlensed galaxies when ALMA is in full operation. (Abridged).

THE PHYSICS OF THE FAR-INFRARED-RADIO CORRELATION. I. CALORIMETRY, CONSPIRACY, AND IMPLICATIONS

(Abridged) The far-infrared (FIR) and radio luminosities of star-forming galaxies are linearly correlated over a very wide range in star formation rate, from normal spirals like the Milky Way to the most intense starbursts. Using one-zone models of cosmic ray (CR) injection, cooling, and escape in star-forming galaxies, we attempt to reproduce the observed FIR-radio correlation over its entire span. We show that ~2% of the kinetic energy from supernova explosions must go into primary CR electrons and that ~10 - 20% must go into primary CR protons. Secondary electrons and positrons are likely comparable to or dominate primary electrons in dense starburst galaxies. We discuss the implications of our models for the magnetic field strengths of starbursts, the detectability of starbursts by Fermi, and cosmic ray feedback. Overall, our models indicate that both CR protons and electrons escape from low surface density galaxies, but lose most of their energy before escaping dense starbursts. The FIR-radio correlation is caused by a combination of the efficient cooling of CR electrons (calorimetry) in starbursts and a conspiracy of several factors. For lower surface density galaxies, the decreasing radio emission caused by CR escape is balanced by the decreasing FIR emission caused by the low effective UV dust opacity. In starbursts, bremsstrahlung, ionization, and Inverse Compton cooling decrease the radio emission, but they are countered by secondary electrons/positrons and the decreasing critical synchrotron frequency, which both increase the radio emission. Our conclusions hold for a broad range of variations on our fiducial model.

ASPITZER-SELECTED GALAXY CLUSTER ATz= 1.62

We report the discovery of a galaxy cluster at z=1.62 located in the Spitzer Wide-Area Infrared Extragalactic survey XMM-LSS field. This structure was selected solely as an overdensity of galaxies with red Spitzer/IRAC colors, satisfying [3.6]-[4.5] > -0.1 AB mag. Photometric redshifts derived from Subaru XMM Deep Survey (BViz-bands), UKIRT Infrared Deep Survey-Ultra-Deep Survey (UKIDSS-UDS, JK-bands), and from the Spitzer Public UDS survey (3.6-8.0 micron) show that this cluster corresponds to a surface density of galaxies at z ~ 1.6 that is more than 20 sigma above the mean at this redshift. We obtained optical spectroscopic observations of galaxies in the cluster region using IMACS on the Magellan telescope. We measured redshifts for seven galaxies in the range z=1.62-1.63 within 2.8 arcmin (<1.4 Mpc) of the astrometric center of the cluster. A posteriori analysis of the XMM data in this field reveal a weak (4 sigma) detection in the [0.5-2 keV] band compatible with the expected thermal emission from such a cluster. The color-magnitude diagram of the galaxies in this cluster shows a prominent red-sequence, dominated by a population of red galaxies with (z-J) > 1.7 mag. The photometric redshift probability distributions for the red galaxies are strongly peaked at z=1.62, coincident with the spectroscopically confirmed galaxies. The rest-frame (U-B) color and scatter of galaxies on the red-sequence are consistent with a mean luminosity-weighted age of 1.2 +/- 0.1 Gyr, yielding a formation redshift z_f = 2.35 +/- 0.10, and corresponding to the last significant star-formation period in these galaxies.

Abell 611

Aims. The Large Binocular Cameras (LBC) are two twin wide field cameras (FOV ~ 23'x 25') mounted at the prime foci of the 8.4m Large Binocular Telescope (LBT). We performed a weak lensing analysis of the z=0.288 cluster Abell 611 on g-band data obtained by the blue-optimized Large Binocular Camera in order to estimate the cluster mass. Methods. Due to the complexity of the PSF of LBC, we decided to use two different approaches, KSB and Shapelets, to measure the shape of background galaxies and to derive the shear signal produced by the cluster. Then we estimated the cluster mass with both aperture densitometry and parametric model fits. Results. The combination of the large aperture of the telescope and the wide field of view allowed us to map a region well beyond the expected virial radius of the cluster and to get a high surface density of background galaxies (23 galaxies/arcmin^2). This made possible to estimate an accurate mass for Abell 611. We find that the mass within 1.5 Mpc is: $(8\pm3)\times 10^{14} M_\odot$ from the aperture mass technique and $(5\pm1)\times 10^{14} M_\odot$ using the model fitting by a NFW mass density profile, for both Shapelets and KSB methods. This analysis demonstrates that LBC is a powerful instrument for weak gravitational lensing studies.

THE EVOLVING RELATIONS BETWEEN SIZE, MASS, SURFACE DENSITY, AND STAR FORMATION IN 3 × 104GALAXIES SINCEz= 2

The presence of massive, compact, quiescent galaxies at z>2 presents a major challenge for theoretical models of galaxy formation and evolution. Using one of the deepest large public near-IR surveys to date, we investigate in detail the correlations between star formation and galaxy structural parameters (size, stellar mass, and surface density) from z=2 to the present. At all redshifts, massive quiescent galaxies (i.e. those with little or no star formation) occupy the extreme high end of the surface density distribution and follow a tight mass-size correlation, while star-forming galaxies show a broad range of both densities and sizes. Conversely, galaxies with the highest surface densities comprise a nearly-homogeneous population with little or no ongoing star formation, while less dense galaxies exhibit high star-formation rates and varying levels of dust obscuration. Both the sizes and surface densities of quiescent galaxies evolve strongly from z=2-0; we parameterize this evolution for both populations with simple power law functions and present best-fit parameters for comparison to future theoretical models. Higher-mass quiescent galaxies undergo faster structural evolution, consistent with previous results. Interestingly, star-forming galaxies' sizes and densities evolve at rates similar to those of quiescent galaxies. It is therefore possible that the same physical processes drive the structural evolution of both populations, suggesting that "dry mergers" may not be the sole culprit in this size evolution.

The Great Observatories Origins Deep Survey

We present the final public data release of the VLT/ISAAC near-infrared imaging survey in the GOODS-South field. The survey covers an area of 172.5, 159.6 and 173.1 arcmin^2 in the J, H, and Ks bands, respectively. For point sources total limiting magnitudes of J=25.0, H=24.5, and Ks=24.4 (5 sigma, AB) are reached within 75% of the survey area. Thus these observations are significantly deeper than the previous EIS Deep Public Survey which covers the same region. The image quality is characterized by a point spread function ranging between 0.34 arcsec and 0.65 arcsec FWHM. The images are registered with an accuracy of ~0.06 arcsec RMS over the whole field. The overall photometric accuracy, including all systematic effects, adds up to 0.05 mag. The data are publicly available from the ESO science archive facility. We define a catalog of Ks-selected sources which contains JHKs photometry for 7079 objects. We briefly discuss the resulting color distributions in the context of available redshift data. Furthermore, we estimate the completeness fraction and relative contamination due to spurious detections for source catalogs extracted from the survey data. With respect to previous deep near-infrared surveys, the surface density of faint galaxies has been established with unprecedented accuracy by virtue of the unique combination of depth and area of this survey. We derived galaxy number counts over eight magnitudes in flux up to J=25.25, H=25.0, Ks=25.25 (in the AB system). Very similar faint-end logarithmic slopes between 0.24 and 0.27 per mag were measured in the three bands. We found no evidence for a significant change in the slope of the logarithmic galaxy number counts at the faint end.

Cross-correlation of diffuse synchrotron and large-scale structures

We explore for the first time the method of cross-correlation of radio synchrotron emission and tracers of large-scale structure in order to detect the diffuse IGM/WHIM. We performed a cross-correlation of a 34 x 34 degree area of 2MASS galaxies for two redshift slices (0.03 < z < 0.04 and 0.06 < z < 0.07) with the corresponding region of the 1.4 GHz Bonn survey. For this analysis, we assumed that the synchrotron surface brightness is linearly proportional to surface density of galaxies. We also sampled the cross-correlation function using 24 distant fields of the same size from the Bonn survey, to better assess the noise properties. Though we obtained a null result, we found that by adding a signal weighted by the 2MASS image with a filament (peak) surface brightness of 1 (7) mK and 7 (49) mK would produce a 3 sigma positive correlation for the 0.03 < z < 0.04 and 0.06 < z < 0.07 redshift slices respectively. These detection thresholds correspond to minimum energy magnetic fields as low as 0.2 microG, close to some theoretical expectations for filament field values. This injected signal is also below the rms noise of the Bonn survey, and demonstrates the power of this technique and its utility for upcoming sensitive continuum surveys such as GALFACTS at Arecibo and those planned with the Murchison Widefield Array (MWA).

A photometric study of the field around the candidate recoiling/binary black hole SDSS J092712.65+294344.0

We present a photometric FUV to Ks-band study of the field around quasar SDSS J092712.65+294344.0. The SDSS spectrum of this object shows various emission lines with two distinct redshifts, at z=0.699 and z=0.712. Because of this peculiar spectroscopic feature this source has been proposed as a candidate recoiling or binary black hole. A third alternative model involves two galaxies moving in the centre of a rich galaxy cluster. Here we present a study addressing the possible presence of such a rich cluster of galaxies in the SDSS J092712.65+294344.0 field. We observed the 3.6x2.6 square arcmin field in the Ks-band and matched the NIR data with the FUV and NUV images in the GALEX archive and the ugriz observations in the SDSS. From various colour-colour diagrams we were able to classify the nature of 32 sources, only 6-11 of which have colours consistent with galaxies at z~0.7. We compare these numbers with the surface density of galaxies, stars & quasars, and the expectations for typical galaxy clusters both at low and high redshift. Our study shows that the galaxy cluster scenario is in clear disagreement with the new observations.

GMASS ultradeep spectroscopy of galaxies at z ~ 2

We present a study of a galaxy overdensity at z=1.6, Cl 0332-2742, uncovered in the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). We conservatively estimate the overdensity in redshift space for the spike, containing 42 galaxies at z=1.6, to be 8.3+/-1.5 and find a velocity dispersion of 500 km/s. A map of the surface density of galaxies at z=1.6 in the GMASS field shows that its structure is irregular. The differences in the physical properties of Cl 0332-2742 member and field galaxies agree with the latest hierarchical galaxy formation models: for overdensity members, the star formation rate (SFR), and specific SFR, is approximately 50% lower than for the field galaxies; overdensity galaxies are twice the age, on average, of field galaxies; and there is a higher proportion of both massive (M>10^{10.7} M_sol), and early-type galaxies, inside Cl 0332-2742 than in the field. Among the 42 members, 7 have spectra consistent with being passively evolving, massive galaxies. In a z-J colour-magnitude diagram, the photometric data of these early-type galaxies are in close agreement with a theoretical red sequence of a galaxy cluster at redshift z=1.6, which formed most of its stars in a short burst of star formation at z~3. We conclude that the redshift spike at z=1.6 in the GMASS field represents a sheet-like structure in the cosmic web and the area with the highest surface density within this structure, containing already seven passively evolving galaxies, will evolve into a cluster of galaxies at a later time.

ENVIRONMENTAL EFFECTS ON THE STAR FORMATION ACTIVITY IN GALAXIES ATz≃ 1.2 IN THE COSMOS FIELD

We investigate the relation between the star formation activity in galaxies and environment at z ≃ 1.2 in the Cosmic Evolution Survey field, using the fraction of [O II] emitters and the local galaxy density. The fraction of [O II] emitters appears to be almost constant over the surface density of galaxies between 0.2 and 10 Mpc^(–2). This trend is different from that seen in the local universe where the star formation activity is weaker in higher density regions. To understand this difference between z ~ 1 and z ~ 0, we study the fraction of non-isolated galaxies as a function of local galaxy density. We find that the fraction of non-isolated galaxies increases with increasing density. Our results suggest that the star formation in galaxies at z ~ 1 is triggered by galaxy interaction and/or mergers.

ABELL 1201: THE ANATOMY OF A COLD FRONT CLUSTER FROM COMBINED OPTICAL AND X-RAY DATA

We present a combined X-ray and optical analysis of the cold front cluster Abell 1201 using archival Chandra, data and multi-object spectroscopy taken with the 3.9m Anglo Australian and 6.5m Multiple Mirror Telescopes. This paper represents the first in a series presenting a study of a sample of cold front clusters selected from the Chandra, archives with the aim of relating cold fronts to merger activity, understanding the dynamics of mergers and their effect on the cluster constituents. The Chandra X-ray imagery of Abell 1201 reveals two conspicuous surface brightness discontinuities, which are shown to be cold fronts, and a remnant core structure. Temperature maps reveal a complex multi-phase temperature structure with regions of hot gas interspersed with fingers of cold gas. Our optical analysis is based on a sample of 321 confirmed members, whose mean redshift is z=0.1673 +/- 0.0002 and velocity dispersion is 778 +/- 36 km/s. We search for dynamical substructure and find clear evidence for multiple localized velocity substructures coincident with over-densities in the galaxy surface density. Most notably, we find structure coincident with the remnant X-ray core. Despite the clear evidence for dynamical activity, we find the peculiar velocity distribution does not deviate significantly from Gaussian. We apply two-body dynamical analyses in order to assess which of the substructures are bound, and thus dynamically important in terms of the cluster merger history. We propose that the cold fronts in Abell 1201 are a consequence of its merger with a smaller subunit, which has induced gas motions that gave rise to `sloshing' cold fronts. Abell 1201 illustrates the value of combining multi-wavelength data and multiple substructure detection techniques when attempting to ascertain the dynamical state of a cluster.

Probing the large-scale structure around the most distant galaxy clusters from the massive cluster survey

We present maps of the cosmic large-scale structure around the twelve most distant galaxy clusters from the Massive Cluster Survey (MACS) as traced by the projected surface density of galaxies on the cluster red sequence. Taken with the Suprime-Cam wide-field camera on the Subaru telescope, the images used in this study cover a 27x27 arcmin^2 area around each cluster, corresponding to 10 x 10 Mpc^2 at the median redshift of z = 0.55 of our sample. We directly detect satellite clusters and filaments extending over the full size of our imaging data in the majority of the clusters studied, supporting the picture of mass accretion via infall along filaments suggested by numerical simulations of the growth of clusters and the evolution of large-scale structure. A comparison of the galaxy distribution near the cluster cores with the X-ray surface brightness as observed with Chandra reveals, in several cases, significant offsets between the gas and galaxy distribution, indicative of ongoing merger events. The respective systems are ideally suited for studies of the dynamical properties of gas, galaxies, and dark matter. In addition, the large-scale filaments viewed at high contrast in these MACS clusters are prime targets for the direct detection and study of the warm-hot intergalactic medium (WHIM).

Pixelation Effects in Weak Lensing

ABSTRACTWeak gravitational lensing can be used to investigate both dark matter and dark energy but requires accurate measurements of the shapes of faint, distant galaxies. Such measurements are hindered by the finite resolution and pixel scale of digital cameras. We investigate the optimum choice of pixel scale for a space‐based mission, using the engineering model and survey strategy of the proposed Supernova Acceleration Probe as a baseline. We do this by simulating realistic astronomical images containing a known input shear signal and then attempting to recover the signal using the Rhodes, Refregier, & Groth algorithm. We find that the quality of shear measurement is always improved by smaller pixels. However, in practice, telescopes are usually limited to a finite number of pixels and operational life span, so the total area of a survey increases with pixel size. We therefore fix the survey lifetime and the number of pixels in the focal plane while varying the pixel scale, thereby effectively varying the survey size. In a pure trade‐off for image resolution versus survey area, we find that measurements of the matter power spectrum would have minimum statistical error with a pixel scale of 0.09″ for a 0.14″ FWHM point‐spread function (PSF). The pixel scale could be increased to ∼0.16″ if images dithered by exactly half‐pixel offsets were always available. Some of our results do depend on our adopted shape measurement method and should be regarded as an upper limit: future pipelines may require smaller pixels to overcome systematic floors not yet accessible, and, in certain circumstances, measuring the shape of the PSF might be more difficult than those of galaxies. However, the relative trends in our analysis are robust, especially those of the surface density of resolved galaxies. Our approach thus provides a snapshot of potential in available technology, and a practical counterpart to analytic studies of pixelation, which necessarily assume an idealized shape measurement method.

Young stellar populations in early-type galaxies in the SDSS

AbstractWe use a purely data-driven rectified factor analysis to identify early-type galaxies with young (≲ 4 Gyr) stellar populations in the Sloan Digital Sky Survey Spectroscopic Catalogue. We call these galaxies E+F galaxies, analogous to E+A galaxies. These galaxies lie in the ‘Green Valley’, between the blue cloud and the red sequence on the colour-magnitude diagram. As such, these galaxies may represent an important transient stage in the evolution of galaxies from blue and star-forming to red and passive. We investigate the distribution in projected local galaxy surface density of the E+F galaxies, and compare it with the environment of early-type and E+A galaxies. We find that i) the E+A distribution peaks strongly in projected local galaxy surface density, Σ5, at ~ 0.1−0.2 Mpc−2, ii) early-types have a flatter peak at ~ 0.06−0.2 Mpc−2, iii) the E+Fs lie somewhere in between, and iv) the distributions of the models do not agree well with the data, peaking at higher densities, and under-predicting the number of E+As at low (Σ5 &lt; 0.3 Mpc−2) densities. The dearth of E+A and E+F galaxies in dense environments confirms that E+A and E+F galaxies are most likely the products of galaxy-galaxy merging or interactions, rather than star-forming galaxies whose star formation has been quenched by processes unique to dense environments, such as ram-pressure stripping or galaxy harassment. The similarity of the environments in which the E+F population and the E+A galaxy sample are found, together with the spectral evidence, suggests that E+F galaxies are E+A galaxies, which have evolved by a further ~ one to a few Gyr.

Discovery of New Faint Radio Emission on 8o to 3′ Scales in the Coma Field, and Some Galactic and Extragalactic Implications

We present a deep, 8$\degr$ diameter, 0.4 GHz radio image using a first time combination of the NAIC Arecibo 305-m telescope in Puerto Rico, and the wide-angle interferometer at the Dominion Radio Astrophysical Observatory at Penticton, Canada. Our observations are centered on the Coma Cluster of galaxies in the ``Great Wall'' of galaxies near the North Galactic Pole. The complementary nature of these two instruments enables us to produce a distortion-free image that is sensitive to radiation on scales from 8$\degr$ down to that of an individual galaxy halo at the 100 Mpc distance of the Great Wall. Newly revealed patches of distributed radio ``glow'' are seen well above the detection limit. One prominent such area coincides with groupings of radio galaxies near the Coma cluster, and indicates intergalactic IGM magnetic fields in the range 0.2 to 0.4 $\mu$G on scales of up to $\sim$ 4 Mpc. Other patches of diffuse emission, not previously explored at these high latitudes on arcminute scales, probably contain Galactic ``cirrus''. A striking anticorrelation is found between low-level diffuse radio glow and some regions of enhanced optical galaxy surface density, suggesting that cosmological Large Scale Structure (LSS), normally defined by the baryonic (or dark) matter density, is not {\it uniquely} traced by faint continuum radio glow. Rather, intergalactic diffuse synchrotron radiation represents IGM magnetic and Cosmic ray energy density, instead of matter density. The diffuse, arcminute-level structures over a large region of sky are potentially important pathfinders to CMB foreground radiation on high multipole scales.

The Effect of FIR Emission from SDSS Galaxies on the SFD Galactic Extinction Map

Abstract We compare the most successful and widely used map of Galactic dust extinction, provided by Schlegel, Finkbeiner, and Davis (1998, hereafter SFD), to the galaxy number counts in the Sloan Digital Sky Survey (SDSS) photometric/spectroscopic DR4 sample. We divide the SDSS survey area into 69 disjoint subregions according to the dust extinction provided by SFD and compare the surface number density of galaxies in each subregion. As expected, the galaxy surface number density decreases with increasing extinction, but only for SFD extinction values above about 0.1 to 0.2 magnitudes (depending on the band). At lower values of the SFD extinction, we find that the sky surface density of galaxies increases with increasing extinction, precisely the opposite of the effect expected from Galactic dust. We also find that the average color of the SDSS photometric galaxy sample is slightly bluer at higher SFD extinctions in this regime, again the opposite of the effect expected from Galactic dust. Even though these anomalies occur only for sight-lines with low SFD extinction values, they affect approximately 68% of the high galactic latitude sky in which galaxies and their clustering properties are normally studied. Although it would be possible to explain these effects with a mysterious component of Galactic dust, which is anti-correlated with the 100$\mu$m flux on which the SFD extinction map is based, this model is not physically plausible. Moreover, we find that the surface number density of SDSS photometric quasars does not show any similar effect, as would be expected if the explanation were an unknown Galactic dust component. Considering these results, we suggest that the far infrared (FIR) brightness of the sky in regions of true low dust extinction is significantly “contaminated” by the FIR emission from background galaxies. We show that such an explanation is both qualitatively and quantitatively consistent with the available data. Based on this interpretation we conclude that systematic errors in the SFD extinction map due to extragalactic FIR emission are quite small, on the order hundredths of a magnitude, but nevertheless statistically detectable. Unfortunately, however, these errors are also entangled in a complex way with a signal of great interest to many “precision cosmology” applications, namely the large-scale clustering of galaxies.

The PSCz dipole revisited

We re-examine the gravitational acceleration (dipole) induced on the Local Group of galaxies by the Infrared Astronomical Satellite (IRAS) galaxy distribution of the Point Source Catalogue redshift survey (PSCz). We treat the cirrus-affected low galactic latitudes by utilizing a spherical harmonic expansion of the galaxy surface density field up to the octapole order. We find strong indications for significant contributions to the Local Group motion from depths up to $\sim 185$ $h^{-1}$ Mpc and possible contribution even from $\sim 210$ $h^{-1}$ Mpc, in agreement with the recent analysis of Kocevski & Ebeling of a whole sky X-ray cluster survey.What changes with respect to the previous PSCz dipole analyses is: (a) the large-scale dipole contributions and (b) an increase of the overall dipole amplitude due to the important contribution of the local volume ($\mincir 4 h^{-1}$Mpc), which we now take into account. This results in a lower value of the $\beta (\equiv \Omega_{\rm m}^{0.6}/b)$ parameter, which we find to be $\beta_{\rm IRAS} \simeq 0.49$ in real space. Therefore, for the concordance cosmological model ($\Omega_{\rm m}=1-\Omega_{\Lambda}=0.3$) the IRAS galaxies bias factor is $b_{\rm IRAS}\simeq 1$ which means that IRAS galaxies are good traces of the underlying matter distribution.

Young stellar populations in early-type galaxies in the Sloan Digital Sky Survey

We use a purely data-driven rectified factor analysis to identify early-type galaxies with recent star formation in DR4 of the SDSS Spectroscopic Catalogue. We compare the spectra and environment of these galaxies with `normal' early-types, and a sample of independently selected E+A galaxies. We calculate the projected local galaxy surface density (Sigma_5 and Sigma_10) for each galaxy in our sample, and find that the dependence, on projected local density, of the properties of E+As is not significantly different from that of early-types with young stellar populations, dropping off rapidly towards denser environments, and flattening off at densities 10% of the stellar mass in these galaxies. This, together with the similarity of the environments in which this `E+F' population and the E+A galaxy sample are found, suggests that E+F galaxies used to be E+A galaxies, but have evolved by a further ~ one to a few Gyr. Our factor analysis is sensitive enough to identify this hidden population. (Abridged)

The effect of local galaxy surface density on star formation for H I selected galaxies

We present the result of investigations into two theories to explain the star formation rate (SFR)-density relationship. For regions of high galaxy density, either there are fewer star-forming galaxies or galaxies capable of forming stars are present but some physical process is suppressing their star formation. We use H I Parkes All-Sky Survey's (HIPASS) HI detected galaxies and infrared and radio fluxes to investigate SFRs and efficiencies with respect to local surface density. For nearby (vel < 10 000 km s(-1)) H I galaxies, we find a strong correlation between H I mass and SFR. The number of H I galaxies decreases with increasing local surface density. For H I galaxies (1000 < vel < 6000 km s(-1)), there is no significant change in the SFR or the efficiency of star formation with respect to local surface density. We conclude that the SFR-density relation is due to a decrease in the number of H I star-forming galaxies in regions of high galaxy density and not to the suppression of star formation.

The great observatories origins deep survey

Aims. We present the final public data release of the VLT/ISAAC near-infrared imaging survey in the GOODS-South field. The survey covers an area of 172.5, 159.6 and 173.1 arcmin in the J, H, and Ks bands, respectively. For point sources total limiting magnitudes of J = 25.0, H = 24.5, and Ks = 24.4 (5σ, AB) are reached within 75% of the survey area. Thus these observations are significantly deeper than the previous EIS Deep Public Survey which covers the same region. The image quality is characterized by a point spread function ranging between 0.34′′ and 0.65′′ FWHM. The images are registered to a common astrometric grid defined by the GSC 2 with an accuracy of ∼0.06′′ RMS over the whole field. The overall photometric accuracy, including all systematic effects, adds up to 0.05 mag. The data are publicly available from the ESO science archive facility. Methods. We describe the data reduction, the calibration, and the quality control process. The final data set is characterized in terms of astrometric and photometric properties, including the PSF and the curve of growth. We establish an empirical model for the sky background noise in order to quantify the variation of limiting depth and statistical photometric errors over the survey area. We define a catalog of Ks-selected sources which contains JHKs photometry for 7079 objects. Differential aperture corrections were applied to the color measurements in order to avoid possible biases as a result of the variation of the PSF. We briefly discuss the resulting color distributions in the context of available redshift data. Furthermore, we estimate the completeness fraction and relative contamination due to spurious detections for source catalogs extracted from the survey data. For this purpose, an empirical study based on a deep Ks image of the Hubble Ultra Deep Field is combined with extensive image simulations. Results. With respect to previous deep near-infrared surveys, the surface density of faint galaxies has been established with unprecedented accuracy by virtue of the unique combination of depth and area of this survey. We derived galaxy number counts over eight magnitudes in flux up to J = 25.25, H = 25.0, Ks = 25.25 (in the AB system). Very similar faint-end logarithmic slopes between 0.24 and 0.27 mag−1 were measured in the three bands. We found no evidence for a significant change in the slope of the logarithmic galaxy number counts at the faint end.