S. di Serego Alighieri

Passively Evolving Early-Type Galaxies at 1.4 ≲ z ≲ 2.5 in the Hubble Ultra Deep Field*

We report on a complete sample of seven luminous early-type galaxies in the Hubble Ultra Deep Field (UDF) with spectroscopic redshifts between 1.39 and 2.47, and to KAB 1:4. Low-resolution spectra of these objects have been extracted from the Hubble Space Telescope (HST) ACS grism data taken over the UDF by the Grism ACS Program for Extragalactic Science (GRAPES) project. Redshifts for the seven galaxies have been identified based on the UV feature at rest frame 2640 < k < 2850 8. This feature is mainly due to a combination of Fe ii ,M gi ,a nd Mgii absorptions, which are characteristic of stellar populations dominated by stars older than � 0.5 Gyr. The redshift identification and the passively evolvingnatureofthesegalaxiesisfurthersupportedbythephotometricredshiftsandbytheoverallspectralenergy distribution (SED), with the ultradeep HST ACS NICMOS imaging revealing compact morphologies typical of

DYNAMICAL MASSES OF EARLY-TYPE GALAXIES AT z ∼ 2: ARE THEY TRULY SUPERDENSE?*

We measured stellar velocity dispersions σ and derived dynamical masses of nine massive (M ≈ 10 11 M� ) earlytype galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4 z 2.0. The σ are based on individual spectra for two galaxies at z ≈ 1.4 and on a stacked spectrum for seven galaxies with 1.6 <z< 2.0, with 202 hr of exposure at the ESO Very Large Telescope. We constructed detailed axisymmetric dynamical models for the objects, based on the Jeans equations, taking the observed surface brightness (from deep HST/ACS observations), point-spread function, and slit effects into account. Our dynamical masses MJeans agree within 30% with virial estimates Mvir = 5 × Reσ 2 /G, although the latter tend to be smaller. Our MJeans also agrees within a factor 2 with the Mpop previously derived using stellar population models and 11 bands photometry. This confirms that the galaxies are intrinsically massive. The inferred mass-to-light ratios (M/L)U in the very age-sensitive rest-frame U band are consistent with passive evolution in the past ∼ 1G yr (formation redshift zf ∼ 3). A “bottom-light” stellar initial mass function appears to be required to ensure close agreement betweenMJeans andMpop at z ∼ 2, as it does at z ∼ 0. The GMASS ETGs are on average more dense than their local counterpart. However, a few percent of local ETGs of similar dynamical masses also have comparable σ and mass surface density Σ50 inside Re.

The dust scaling relations of the Herschel Reference Survey

We combine new Herschel/SPIRE sub-millimeter observations with existing multiwavelength data to investigate the dust scaling relations of the Herschel Reference Survey, a magnitude-, volume-limited sample of similar to 300 nearby galaxies in different environments. We show that the dust-to-stellar mass ratio anti-correlates with stellar mass, stellar mass surface density and NUV - r colour across the whole range of parameters covered by our sample. Moreover, the dust-to-stellar mass ratio decreases significantly when moving from late-to early-type galaxies. These scaling relations are similar to those observed for the Hi gas-fraction, supporting the idea that the cold dust is tightly coupled to the cold atomic gas component in the interstellar medium. We also find a weak increase of the dust-to-Hi mass ratio with stellar mass and colour but no trend is seen with stellar mass surface density. By comparing galaxies in different environments we show that, although these scaling relations are followed by both cluster and field galaxies, Hi-deficient systems have, at fixed stellar mass, stellar mass surface density and morphological type systematically lower dust-to-stellar mass and higher dust-to-Hi mass ratios than Hi-normal/field galaxies. This provides clear evidence that dust is removed from the star-forming disk of cluster galaxies but the effect of the environment is less strong than what is observed in the case of the Hi disk. Such effects naturally arise if the dust disk is less extended than the Hi and follows more closely the distribution of the molecular gas phase, i.e., if the dust-to-atomic gas ratio monotonically decreases with distance from the galactic center.

Near-Infrared Bright Galaxies at z ≃ 2. Entering the Spheroid Formation Epoch?*

Spectroscopic redshifts have been measured for nine K-band luminous galaxies at 1.7 < z < 2.3, selected with Ks < 20 in the K20 survey region of the Great Observatories Origins Deep Survey (GOODS) area. Star formation rates (SFRs) of ~100-500 M? yr-1 are derived when dust extinction is taken into account. The fitting of their multicolor spectral energy distributions indicates stellar masses of M 1011 M? for most of the galaxies. Their rest-frame UV morphology is highly irregular, suggesting that merging-driven starbursts are going on in these galaxies. Morphologies tend to be more compact in the near-IR, a hint for the possible presence of older stellar populations. Such galaxies are strongly clustered, with seven out of nine belonging to redshift spikes, which indicates a correlation length of r0 ~ 9-17 h-1 Mpc (1 ? range). Current semianalytical models of galaxy formation appear to underpredict by a large factor (30) the number density of such a population of massive and powerful starburst galaxies at z ~ 2. The high masses and SFRs, together with the strong clustering, suggest that at z ~ 2 we may have started to explore the major formation epoch of massive early-type galaxies.

An Overdensity of Galaxies at z = 5.9 ? 0.2 in the Hubble Ultra Deep Field Confirmed Using the ACS Grism

We present grism spectra taken with the Advanced Camera for Surveys (ACS) to identify 29 red sources with (i775 - z850) ? 0.9 in the Hubble Ultra Deep Field (HUDF). Of these, 23 are found to be galaxies at redshifts between z = 5.4 and 6.7, identified by the break at 1216 ? due to intergalactic medium (IGM) absorption; two are late-type dwarf stars with red colors; and four are galaxies with colors and spectral shapes similar to dust-reddened or old galaxies at redshifts z ? 1-2. This constitutes the largest uniform, flux-limited sample of spectroscopically confirmed galaxies at such faint fluxes (z850 ? 27.5). Many are also among the most distant spectroscopically confirmed galaxies (at redshifts up to z = 6.7). We find a significant overdensity of galaxies at redshifts z = 5.9 ? 0.2. Nearly two-thirds of the galaxies in our sample (15/23) belong to this peak. Taking into account the selection function and the redshift sensitivity of the survey, we get a conservative overdensity of at least a factor of 2 along the line of sight. The galaxies found in this redshift peak are also localized in the plane of the sky in a nonrandom manner, occupying about half of the ACS chip. Thus the volume overdensity is a factor of 4. The star formation rate derived from detected sources in this overdense region is sufficient to reionize the local IGM.

The Herschel Reference Survey: dust in early-type galaxies and across the Hubble Sequence

We present Herschel observations of 62 early-type galaxies (ETGs), including 39 galaxies morphologically classified as S0+S0a and 23 galaxies classified as ellipticals using SPIRE at 250, 350, and 500 mu m as part of the volume-limited Herschel Reference Survey (HRS). We detect dust emission in 24% of the ellipticals and 62% of the S0s. The mean temperature of the dust is \textless T-d \textgreater = 23.9 +/- 0.8 K, warmer than that found for late-type galaxies in the Virgo Cluster. The mean dust mass for the entire detected early-type sample is log M-d = 6.1 +/- 0.1 M-circle dot with a mean dust-to-stellar-mass ratio of log(M-d/M-*) = -4.3 +/- 0.1. Including the non-detections, these parameters are log M-d = 5.6 +/- 0.1 and log(M-d/M-*) = -5.1 +/- 0.1, respectively. The average dust-to-stellar-mass ratio for the early-type sample is fifty times lower, with larger dispersion, than the spiral galaxies observed as part of the HRS, and there is an order-of-magnitude decline in M-d/M-* between the S0s and ellipticals. We use UV and optical photometry to show that virtually all the galaxies lie close to the red sequence yet the large number of detections of cool dust, the gas-to-dust ratios, and the ratios of far-infrared to radio emission all suggest that many ETGs contain a cool interstellar medium similar to that in late-type galaxies. We show that the sizes of the dust sources in S0s are much smaller than those in early-type spirals and the decrease in the dust-to-stellar-mass ratio from early-type spirals to S0s cannot simply be explained by an increase in the bulge-to-disk ratio. These results suggest that the disks in S0s contain much less dust (and presumably gas) than the disks of early-type spirals and this cannot be explained simply by current environmental effects, such as ram-pressure stripping. The wide range in the dust-to-stellar-mass ratio for ETGs and the lack of a correlation between dust mass and optical luminosity suggest that much of the dust in the ETGs detected by Herschel has been acquired as the result of interactions, although we show these are unlikely to have had a major effect on the stellar masses of the ETGs. The Herschel observations tentatively suggest that in the most massive systems, the mass of interstellar medium is unconnected to the evolution of the stellar populations in these galaxies.

The evolution of early-type galaxies at z ∼ 1 from the K20 survey

We have performed VLT spectroscopy of an almost complete sample of 18 early-type galaxies with

New spectroscopic redshifts from the CDFS and a test of the cosmological relevance of the GOODS-South field

0.88\leq z\leq 1.3

Kinematically quiet haloes around z∼ 2.5 radio galaxies. Keck spectroscopy

plus two at

Dust spectral energy distributions of nearby galaxies: an insight from the Herschel Reference Survey

z=0.67