The Star Formation Epoch of the Most Massive Early-Type Galaxies

We present new Keck spectroscopy of early-type galaxies in three galaxy clusters at z~0.5. We focus on the fundamental plane (FP) relation, and combine the kinematics with structural parameters determined from HST images. The galaxies obey clear FP relations, which are offset from the FP of the nearby Coma cluster due to passive evolution of the stellar populations. The z~0.5 data are combined with published data for 11 additional clusters at 0.18<z<1.28, to determine the evolution of the mean M/L(B) ratio of cluster galaxies with masses M>10^11 M_sun, as implied by the FP. We find dlog(M/L(B))/dz = -0.555+-0.042, stronger evolution than was previously inferred from smaller samples. The observed evolution depends on the luminosity-weighted mean age of the stars in the galaxies, the initial mass function (IMF), selection effects due to progenitor bias, and other parameters. Assuming a normal IMF but allowing for various other sources of uncertainty we find z* = 2.01+-0.20 for the luminosity-weighted mean star formation epoch. The main uncertainty is the slope of the IMF in the range 1-2 Solar masses: we find z* = 4.0 for a top-heavy IMF with slope x=0. The M/L(B) ratios of the cluster galaxies are compared to those of recently published samples of field early-type galaxies at 0.32<z<1.14. Assuming that progenitor bias and the IMF do not depend on environment we find that the present-day age of stars in massive field galaxies is 4.1 +- 2.0 % (~0.4 Gyr) less than that of stars in massive cluster galaxies, consistent with most, but not all, previous studies of local and distant early-type galaxies. This relatively small age difference is surprising in the context of expectations from ``standard'' hierarchical galaxy formation models. [ABRIDGED]Comment: Accepted for publication in ApJ. Minor corrections to match published versio

The A-X infrared bands of Aluminum Oxide in stars: search and new detections

We describe a search for the A-X infrared bands of AlO with a view to better understand the characteristics of this radical. These bands are infrequently encountered in astronomical sources but surprisingly were very prominent in the spectra of two well-known, nova-like variables (V838 Mon and V4332 Sgr) thereby motivating us to explore the physical conditions necessary for their excitation. In this study, we present the detection of A-X bands in the spectra of 13 out of 17 stars, selected on the basis of their J-K colors as potential candidates for detection of these bands. The majority of the AlO detections are in AGB stars viz. 9 OH/IR stars, 2 Mira variables and 2 bright infrared sources. Our study shows that the A-X bands are fairly prevalent in sources with low temperature and O-rich environments. Interesting variation in strength of the AlO bands in one of the sources (IRAS 18530+0817) is reported and the cause for this is examined. Possible applications of the present study are discussed in terms of the role of AlO in alumina dust formation, the scope for estimating the radioactive $^{26}$Al content in AGB stars from the A-X bands, and providing possible targets for further mm/radio studies of AlO which has recently been discovered at millimeter wavelengths.Comment: To appear in Astrophysical Journal (Letters), 14 pages, 2 figure

The Gravitational Lens CFRS03.1077

An exquisite gravitational arc with a radius of 2.1" has been discovered around the z = 0.938 field elliptical galaxy CFRS03.1077 during HST observations of Canada-France Redshift Survey (CFRS) fields. Spectroscopic observations of the arc show that the redshift of the resolved lensed galaxy is z = 2.941. This gravitational lens-source system is well-fitted using the position angle and ellipticity derived from the visible matter distribution and an isothermal mass profile with a mass corresponding to sigma =387+-5 km/s. Surprisingly, given the evidence for passive evolution of elliptical galaxies, this is in good agreement with an estimate based on the fundamental plane for z = 0 ellipticals. This, perhaps, indicates that this galaxy has not shared in the significant evolution observed for average elliptical galaxies at z ~ 1. A second elliptical galaxy with similar luminosity from the CFRS survey, CFRS 14.1311 at z=0.807, is also a lens but in this case the lens model gives a much smaller mass-to-light ratio, i.e., it appears to confirm the expected evolution. This suggests that this pair of field elliptical galaxies may have very different evolutionary histories, a significant result if confirmed. Clearly, CFRS03.1077 demonstrates that these "Einstein rings" are powerful probes of high redshift galaxies.Comment: 11 pages, 5 figures, accepted by Ap.

Gemini Deep Deep Survey VI: Massive Hdelta-strong galaxies at z=1

We show that there has been a dramatic decline in the abundance of massive galaxies with strong Hdelta stellar absorption lines from z=1.2 to the present. These ``Hdelta-strong'', or HDS, galaxies have undergone a recent and rapid break in their star-formation activity. Combining data from the Gemini Deep Deep and the Sloan Digital Sky Surveys to make mass-matched samples (M*>=10^10.2 Msun), with 25 and 50,255 galaxies, respectively), we find that the fraction of galaxies in an HDS phase has decreased from about 50% at z=1.2 to a few percent today. This decrease in fraction is due to an actual decrease in the number density of massive HDS systems by a factor of 2-4, coupled with an increase in the number density of massive galaxies by about 30 percent. We show that this result depends only weakly on the threshold chosen for the Hdelta equivalent width to define HDS systems (if greater than 4 A) and corresponds to a (1+z)^{2.5\pm 0.7} evolution. Spectral synthesis studies of the high-redshift population using the PEGASE code, treating Hdelta_A, EW[OII], Dn4000, and rest-frame colors, favor models in which the Balmer absorption features in massive Hdelta-strong systems are the echoes of intense episodes of star-formation that faded about 1 Gyr prior to the epoch of observation. The z=1.4-2 epoch appears to correspond to a time at which massive galaxies are in transition from a mode of sustained star formation to a relatively quiescent mode with weak and rare star-formation episodes. We argue that the most likely local descendants of the distant massive HDS galaxies are passively evolving massive galaxies in the field and small groups.Comment: 16 pages, 12 figures, 3 tables, uses emulateapj.sty; updated to match the version accepted by ApJ. One figure added, conclusions unchange

Reassessment of the evolution of wheat chromosomes 4A, 5A, and 7B.

Key messageComparison of genome sequences of wild emmer wheat and Aegilops tauschii suggests a novel scenario of the evolution of rearranged wheat chromosomes 4A, 5A, and 7B. Past research suggested that wheat chromosome 4A was subjected to a reciprocal translocation T(4AL;5AL)1 that occurred in the diploid progenitor of the wheat A subgenome and to three major rearrangements that occurred in polyploid wheat: pericentric inversion Inv(4AS;4AL)1, paracentric inversion Inv(4AL;4AL)1, and reciprocal translocation T(4AL;7BS)1. Gene collinearity along the pseudomolecules of tetraploid wild emmer wheat (Triticum turgidum ssp. dicoccoides, subgenomes AABB) and diploid Aegilops tauschii (genomes DD) was employed to confirm these rearrangements and to analyze the breakpoints. The exchange of distal regions of chromosome arms 4AS and 4AL due to pericentric inversion Inv(4AS;4AL)1 was detected, and breakpoints were validated with an optical Bionano genome map. Both breakpoints contained satellite DNA. The breakpoints of reciprocal translocation T(4AL;7BS)1 were also found. However, the breakpoints that generated paracentric inversion Inv(4AL;4AL)1 appeared to be collocated with the 4AL breakpoints that had produced Inv(4AS;4AL)1 and T(4AL;7BS)1. Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 either originated sequentially, and Inv(4AL;4AL)1 was produced by recurrent chromosome breaks at the same breakpoints that generated Inv(4AS;4AL)1 and T(4AL;7BS)1, or Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 originated simultaneously. We prefer the latter hypothesis since it makes fewer assumptions about the sequence of events that produced these chromosome rearrangements

Hubble Space Telescope Imaging of the CFRS and LDSS Redshift Surveys---III. Field elliptical galaxies at 0.2 < z < 1.0

Surface photometry has been performed on a sample of 46 field elliptical galaxies. These galaxies are described well by a deVaucouleurs R^{1/4} profile. The sample was selected from the combined Canada-France and LDSS redshift surveys and spans the range 0.20 < z < 1.00. The relationship between galaxy half-light radius and luminosity evolves such that a galaxy of a given size is more luminous by Delta M_B=-0.97 \pm 0.14 mag at z=0.92 and the mean rest-frame color shifts blueward by Delta (U-V) =-0.68 \pm 0.11 at z=0.92 relative to the local cluster relations. Approximately 1/3 of these elliptical galaxies exhibit [OII] 3727 emission lines with equivalent widths > 15 angstroms indicating ongoing star formation. Estimated star-formation rates imply that \le 5% of the stellar mass in the elliptical galaxy population has been formed since z=1. We see no evidence for a decline in the space density of early-type galaxies with look-back time. The statistics and a comparison with local luminosity functions are both consistent with the view that the population of massive early-type galaxies was largely in place by z~1. This implies that merging is not required since that time to produce the present-day space density of elliptical galaxies.Comment: 21 pages plus 8 figures plus 5 tables. Accepted by Astrophysical Journa

Towards an effective potential for the monomer, dimer, hexamer, solid and liquid forms of hydrogen fluoride

We present an attempt to build up a new two-body effective potential for hydrogen fluoride, fitted to theoretical and experimental data relevant not only to the gas and liquid phases, but also to the crystal. The model is simple enough to be used in Molecular Dynamics and Monte Carlo simulations. The potential consists of: a) an intra-molecular contribution, allowing for variations of the molecular length, plus b) an inter-molecular part, with three charged sites on each monomer and a Buckingham "exp-6" interaction between fluorines. The model is able to reproduce a significant number of observables on the monomer, dimer, hexamer, solid and liquid forms of HF. The shortcomings of the model are pointed out and possible improvements are finally discussed.Comment: LaTeX, 24 pages, 2 figures. For related papers see also http://www.chim.unifi.it:8080/~valle

The Gemini Deep Deep Survey: VIII. When Did Early-type Galaxies Form?

We have used the Hubble Space Telescope's Advanced Camera for Surveys (Ford et al. 2003) to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z \~ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range

The UV colours of high-redshift early-type galaxies: evidence for recent star formation and stellar mass assembly over the last 8 billion years

We combine deep UBVRIzJK photometry from the Multiwavelength Survey by Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a large-scale study of the rest-frame ultraviolet (UV) properties of 674 high-redshift (0.5<z<1) early-type galaxies, drawn from the Extended Chandra Deep Field South (E-CDFS). Galaxy morphologies are determined through visual inspection of Hubble Space Telescope (HST) images taken from the GEMS survey. We harness the sensitivity of the UV to young (<1 Gyr old) stars to quantify the recent star formation history of early-type galaxies across a range of luminosities (-23.5 < M(V) < -18). Comparisons to simple stellar populations forming at high redshift indicate that only ~1.1 percent of early-types in this sample are consistent with purely passive ageing since z=2. Parametrising the recent star formation (RSF) in terms of the mass fraction of stars less than a Gyr old, we find that the early-type population as a whole shows a typical RSF between 5 and 13% in the redshift range 0.5<z<1. Early-types on the UV red sequence show RSF values less than 5% while the reddest early-types are virtually quiescent with RSF values of ~1%. We find compelling evidence that early-types of all luminosities form stars over the lifetime of the Universe, although the bulk of their star formation is already complete at high redshift. This tail-end of star formation is measurable and not negligible, with luminous (-23<M(V)<-20.5) early-types potentially forming 10-15% of their mass since z=1, with their less luminous (M(V)>-20.5) counterparts potentially forming 30-60 percent of their mass in the same redshift range. (abridged)Comment: Submitted to MNRA