Sune Toft

The size evolution of galaxies since z~3: combining SDSS, GEMS, and FIRES

We present the evolution of the luminosity-size and stellar mass-size relations of luminous ( L-V greater than or similar to 3.4 x 10(10) h(70)(-2) L-circle dot) and massive ( M-* greater than or similar to 3 x 10(10) h(70)(-2) M-circle dot) galaxies in the last similar to 11 Gyr. We use very deep near-infrared images of the Hubble Deep Field-South and the MS 1054-03 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 similar to 0.1 to achieve a comprehensive picture of the optical rest-frame size evolution from z = 0 to 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 similar to 3 +/- 0.5 ( +/- 2 sigma) times smaller at z similar to 2: 5 than those we see today. The stellar mass-size relation has evolved less: the mean size at a given stellar mass was similar to 2 +/- 0.5 times smaller at z similar to 2.5, evolving proportionally 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 similar to 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 similar to 2.7 +/- 1.1 times smaller at z similar to 2.5 ( or, put differently, were typically similar to 2.2 +/- 0.7 mag brighter at a given size than they are today), and at a given stellar mass the size has evolved proportionally to ( 1 + z)(-0.45 +/- 0.10).

Hubble Space Telescope and Spitzer Imaging of Red and Blue Galaxies at z ~ 2.5: A Correlation between Size and Star Formation Activity from Compact Quiescent Galaxies to Extended Star-forming Galaxies*

We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2 < z < 3.5 in the FIRES MS 1054 field with red and blue rest-frame optical colors. About half of the galaxies are very compact (effective radii re < 1 kpc) at rest-frame optical wavelengths; the others are extended (1 kpc < re < 10 kpc). For reference, 1 kpc corresponds to 0.12 at z = 2.5 in the adopted cosmology. We separate actively star-forming galaxies from quiescent galaxies by modeling their rest-frame UV-NIR SEDs. The star-forming galaxies span the full range of sizes, while the quiescent galaxies all have re < 2 kpc. In the redshift range where MIPS 24 ?m imaging is a sensitive probe of reradiated dust emission (z < 2.5), the 24 ?m fluxes confirm that the light of the small quiescent galaxies is dominated by old stars, rather than dust-enshrouded star formation or AGN activity. The inferred surface mass densities and velocity dispersions for the quiescent galaxies are very high compared to those in local galaxies. The galaxies follow a Kormendy relation (between surface brightness and size) with approximately the same slope as locally, but shifted to brighter surface brightnesses, consistent with a mean stellar formation redshift of zf ~ 5. This paper demonstrates a direct relation between star formation activity and size at z ~ 2.5 and the existence of a significant population of massive, extremely dense, old stellar systems without readily identifiable counterparts in the local universe.

The multiwavelength survey by yale-chile (musyc): survey design and deep public ubvriz' images and catalogs of the extended hubble deep field south

We present UBVRIz optical images taken with MOSAIC on the CTIO 4 m telescope of the 0.32 deg2 Extended Hubble Deep Field-South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z = 3, active galactic nucleus (AGN) demographics, and Galactic structure. Our methods used for astrometric calibration, weighted image combination, and photometric calibration in AB magnitudes are described. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62,968 objects is complete to a total magnitude of RAB = 25, with R-band counts consistent with results from the literature. We select z 3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4 arcmin-2 and an angular correlation function w(θ) = (2.3 ± 1.0)θ-0.8, consistent with previous findings that high-redshift Lyman break galaxies reside in massive dark matter halos. Our images and catalogs are available online.

The space density and colors of massive galaxies at 2 < z < 3: the predominance of distant red galaxies

Using the deep multiwavelength MUSYC, GOODS, and FIRES surveys we construct a stellar mass-limited sample of galaxies at 2 1011 M☉ distributed over four independent fields with a total area of almost 400 arcmin2. The mean number density of massive galaxies in this redshift range ρ(M > 1011 M☉) = (2.2 ± 0.6) × 10-4 h Mpc-3. We present median values and 25th and 75th percentiles for the distributions of observed RAB magnitudes, observed J - Ks colors, and rest-frame ultraviolet continuum slopes, M/LV ratios, and U - V colors. The galaxies show a large range in all these properties. The median galaxy is faint in the observers optical (RAB = 25.9), red in the observed near-IR (J - Ks = 2.48), has a rest-frame UV spectrum that is relatively flat in Fλ (β = -0.4), and rest-frame optical colors resembling those of nearby spiral galaxies (U - V = 0.62). We determine which galaxies would be selected as Lyman break galaxies (LBGs) or distant red galaxies (DRGs, having J - Ks > 2.3) in this mass-limited sample. By number DRGs make up 69% of the sample, and LBGs 20%, with a small amount of overlap. By mass DRGs make up 77%, and LBGs 17%. Neither technique provides a representative sample of massive galaxies at 2 < z < 3 as they only sample the extremes of the population. As we show here, multiwavelength surveys with high-quality photometry are essential for an unbiased census of massive galaxies in the early universe. The main uncertainty in this analysis is our reliance on photometric redshifts; confirmation of the results presented here requires extensive near-infrared spectroscopy of optically faint samples.

The Rest-Frame Optical Luminosity Functions of Galaxies at 2?z?3.5

We present the rest-frame optical (B, V, and R band) luminosity functions (LFs) of galaxies at 2 ≤ z ≤ 3.5, measured from a K-selected sample constructed from the deep NIR MUSYC, the ultradeep FIRES, and the GOODS-CDFS. This sample is unique for its combination of area and range of luminosities. The faint-end slopes of the LFs at z > 2 are consistent with those at z ~ 0. The characteristic magnitudes are significantly brighter than the local values (e.g., ~1.2 mag in the R band), while the measured values for Φ are typically ~5 times smaller. The B-band luminosity density at z ~ 2.3 is similar to the local value, and in the R band it is ~2 times smaller than the local value. We present the LF of distant red galaxies (DRGs), which we compare to that of non-DRGs. While DRGs and non-DRGs are characterized by similar LFs at the bright end, the faint-end slope of the non-DRG LF is much steeper than that of DRGs. The contribution of DRGs to the global densities down to the faintest probed luminosities is 14%-25% in number and 22%-33% in luminosity. From the derived rest-frame U - V colors and stellar population synthesis models, we estimate the mass-to-light ratios (M/L) of the different subsamples. The M/L ratios of DRGs are ~5 times higher (in the R and V bands) than those of non-DRGs. The global stellar mass density at 2 ≤ z ≤ 3.5 appears to be dominated by DRGs, whose contribution is of order ~60%-80% of the global value. Qualitatively similar results are obtained when the population is split by rest-frame U - V color instead of observed J - K color.

Direct Measurements of the Stellar Continua and Balmer/4000 Å Breaks of Red z > 2 Galaxies: Redshifts and Improved Constraints on Stellar Populations* ** ***

We use near-infrared (NIR) spectroscopy obtained with the GNIRS on Gemini, NIRSPEC on the Keck, and ISAAC on the VLT to study the rest-frame optical continua of three distant red galaxies (with Js - Ks > 2.3) at z > 2. All three galaxy spectra show the Balmer/4000 ? break in the rest-frame optical. The spectra allow us to determine spectroscopic redshifts from the continuum with an estimated accuracy of ?z/(1 + z) ~ 0.001-0.04. These redshifts agree well with the emission-line redshifts for the two galaxies with H? emission. This technique is particularly important for galaxies that are faint in the rest-frame UV, as they are underrepresented in high-redshift samples selected in optical surveys and are too faint for optical spectroscopy. Furthermore, we use the break, continuum shape, and equivalent width of H?, together with evolutionary synthesis models, to constrain the age, star formation timescale, dust content, stellar mass, and star formation rate of the galaxies. Inclusion of the NIR spectra in the stellar population fits greatly reduces the range of possible solutions for stellar population properties. We find that the stellar populations differ greatly among the three galaxies, ranging from a young dusty starburst with a small break and strong emission lines to an evolved galaxy with a strong break and no detected line emission. The dusty starburst galaxy has an age of 0.3 Gyr and a stellar mass of 1 ? 1011 M?. The spectra of the two most evolved galaxies imply ages of 1.3-1.4 Gyr and stellar masses of 4 ? 1011 M?. This large range of properties strengthens our previous, more uncertain results from broadband photometry. Larger samples are required to determine the relative frequency of dusty starbursts and (nearly) passively evolving galaxies at z ~ 2.5.

The Near-Infrared Camera and Multi-Object Spectrometer Ultra Deep Field: Observations, data reduction, and galaxy photometry

This paper describes the observations and data reduction techniques for the version 2.0 images and catalog of the Near-Infrared Camera and Multi-Object Spectrometer Ultra Deep Field (NICMOS UDF) Treasury program. All sources discussed in this paper are based on detections in the combined NICMOS F110W and F160W bands only. The NICMOS images are drizzled to 009 pixel-1 and aligned to the Advanced Camera for Surveys UDF F850LP image, which was rebinned to the same pixel scale. These form the NICMOS version 2.0 UDF images. The catalog sources are chosen with a conservative detection limit to avoid the inclusion of numerous spurious sources. The catalog contains 1293 objects in the 144 × 144 NICMOS subfield of the UDF. The 5 σ signal-to-noise ratio level is an average 06 diameter aperture AB magnitude of 27.7 at 1.1 and 1.6 μm. The catalog sources, listed in order of right ascension, satisfy a minimum signal-to-noise ratio criterion of 1.4 σ in at least seven contiguous pixels of the combined F110W and F160W image.This paper describes the observations and data reduction techniques for the version 2.0 images and catalog of the NICMOS Ultra Deep Field Treasury program. All sources discussed in this paper are based on detections in the combined NICMOS F110W and F160W bands only. The NICMOS images are drizzled to 0.09 arc second pixels and aligned to the ACS UDF F850LP image which was rebinned to the same pixel scale. These form the NICMOS version 2.0 UDF images. The catalog sources are chosen with a conservative detection limit to avoid the inclusion of numerous spurious sources. The catalog contains 1293 objects in the 144 x 144 arc sececonds NICMOS subfield of the UDF. The 5 sigma signal to noise level is an average 0.6 arc second diameter aperture AB magnitude of ~27.7 at 1.1 and 1.6 microns. The catalog sources, listed in order of right ascension, satisfy a minimum signal to noise criterion of 1.4 sigma in at least 7 contiguous pixels of the combined F110W and F160W image

Extinction Curves of Lensing Galaxies out to z = 1

We present a survey of the extinction properties of 10 lensing galaxies, in the redshift range z = 0.04-1.01, using multiply lensed quasars imaged with the ESO VLT in the optical and near-infrared. The multiple images act as standard light sources shining through different parts of the lensing galaxy, allowing for extinction studies by comparison of pairs of images. We explore the effects of systematics in the extinction curve analysis, including extinction along both lines of sight and microlensing, using theoretical analysis and simulations. In the sample, we see variation in both the amount and type of extinction. Of the 10 systems, seven are consistent with extinction along at least one line of sight. The mean differential extinction for the most extinguished image pair for each lens is (V) = 0.56 ± 0.04, using Galactic extinction law parameterization. The corresponding mean V = 2.8 ± 0.4 is consistent with that of the Milky Way at RV = 3.1, where RV = A(V)/E(B - V). We do not see any strong evidence for evolution of extinction properties with redshift. Of the 10 systems, B1152+199 shows the strongest extinction signal of A(V) = 2.43 ± 0.09 and is consistent with a Galactic extinction law with RV = 2.1 ± 0.1. Given the similar redshift distribution of SN Ia hosts and lensing galaxies, a large space-based study of multiply imaged quasars would be a useful complement to future dark energy SN Ia surveys, providing independent constraints on the statistical extinction properties of galaxies up to z ~ 1.

Discovery of a very extended X-ray halo around a quiescent spiral galaxy – The “missing link” of galaxy formation

Abstract Hot gaseous haloes surrounding galaxies and extending well beyond the distribution of stars are a ubiquitous prediction of galaxy formation scenarios. The haloes are believed to consist of gravitationally trapped gas with a temperature of millions of Kelvin. The existence of such hot haloes around massive elliptical galaxies has been established through their X-ray emission. While gas out-flowing from starburst spiral galaxies has been detected, searches for hot haloes around normal, quiescent spiral galaxies have so far failed, casting doubts on the fundamental physics in galaxy formation models. Here we present the first detection of a hot, large-scale gaseous halo surrounding a normal, quiescent spiral galaxy, NGC 5746 , alleviating a long-standing problem for galaxy formation models. In contrast to starburst galaxies, where the X-ray halo can be powered by the supernova energy, there is no such power source in NGC 5746 . The only compelling explanation is that we are here witnessing a galaxy forming from gradually in-flowing hot and dilute halo gas.

Distant Red Galaxies in the Hubble Ultra Deep Field

We take advantage of the Hubble Ultra Deep Field data to study the rest-frame optical and UV morphologies of the novel population of distant red galaxies (DRGs). Six galaxies with J-Ks > 2.3 are found to Ks = 21.5, five of which have photometric redshifts zphot 2, corresponding to a surface density of 0.9 arcmin-2. The surface brightness distributions of the zphot 2 galaxies are better represented by exponential disks than R1/4 laws. Two of the zphot 2 galaxies are extended, while three have compact morphologies. The rest-frame optical morphology of the zphot 2 galaxies is quite different from the rest-frame UV morphology: All the galaxies have red central components that dominate in the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) H160-band images, as well as distinct off-center blue features that show up in (and often dominate) the Advanced Camera for Surveys (ACS) images. The mean measured effective radius of the zphot 2 galaxies is re = 1.9 ? 1.4 kpc, similar (within the errors) to the mean size of Lyman break galaxies at similar redshifts. All the DRGs are resolved in the ACS images, while four are resolved in the NICMOS images. Two of the zphot 2 galaxies are bright X-ray sources and hence host active galactic nuclei (AGNs). One of these galaxies is resolved in the ACS and NICMOS images, which means that the AGN does not dominate its rest-frame UV/optical spectral energy distribution (SED), while the other is unresolved in the NICMOS images and hence could have an AGN-dominated SED. The diverse rest-frame optical and UV morphological properties of DRGs derived here suggest that they have complex stellar populations consisting of both evolved populations, which dominate the mass and the rest-frame optical light, and younger populations that show up as patches of star formation in the rest-frame UV light, in many ways resembling the properties of normal local galaxies. This interpretation is supported by fits to the broadband SEDs, which for all five zphot 2 galaxies are best represented by models with extended star formation histories and substantial amounts of dust.