The Evolution of Rest-Frame K-band Properties of Early-Type Galaxies from z=1 to the Present

We measure the evolution of the rest-frame K-band Fundamental Plane from z=1 to the present by using IRAC imaging of a sample of early-type galaxies in the Chandra Deep Field-South at z~1 with accurately measured dynamical masses. We find that $M/L_K$ evolves as $\Delta\ln{(M/L_K)}=(-1.18\pm0.10)z$, which is slower than in the B-band ($\Delta\ln{(M/L_B)}=(-1.46\pm0.09)z$). In the B-band the evolution has been demonstrated to be strongly mass dependent. In the K-band we find a weaker trend: galaxies more massive than $M=2\times10^{11}M_{\odot}$ evolve as $\Delta\ln{(M/L_K)}=(-1.01\pm0.16)z$; less massive galaxies evolve as $\Delta\ln{(M/L_K)}=(-1.27\pm0.11)z$. As expected from stellar population models the evolution in $M/L_K$ is slower than the evolution in $M/L_B$. However, when we make a quantitative comparison, we find that the single burst Bruzual-Charlot models do not fit the results well, unless large dust opacities are allowed at z=1. Models with a flat IMF fit better, Maraston models with a different treatment of AGB stars fit best. These results show that the interpretation of rest-frame near-IR photometry is severely hampered by model uncertainties and therefore that the determination of galaxy masses from rest-frame near-IR photometry may be harder than was thought before.Comment: 5 pages, 3 figures, Accepted for publication in ApJ

Mass-to-Light Ratios of Field Early-Type Galaxies at z~1 from Ultra-Deep Spectroscopy: Evidence for Mass-dependent Evolution

We present an analysis of the Fundamental Plane for a sample of 27 field early-type galaxies in the redshift range 0.6<z<1.15. The galaxies in this sample have high S/N spectra obtained at the VLT and high resolution imaging from the ACS. We find that the mean evolution in M/L of our sample is $Delta ln (M/L_B) = -1.74+/-0.16z$, with a large galaxy-to-galaxy scatter. This value can be too low by 0.3 due to selection effects, resulting in $Delta ln (M/L_B) = -1.43+/-0.16z$. The strong correlation between M/L and rest-frame color indicates that the observed scatter is not due to measurement errors, but due to intrinsic differences between the stellar populations of the galaxies. This pace of evolution is much faster than the evolution of cluster galaxies. However, we find that the measured M/L evolution strongly depends on galaxy mass. For galaxies with masses $M>2 x 10^11 Msol$, we find no significant difference between the evolution of field and cluster galaxies: $Delta ln (M/L_B) = -1.20+/-0.18z for field galaxies and$Delta ln (M/L_B) = -1.12+/-0.06z$ for cluster galaxies. The relation between the measured M/L evolution and mass is partially due to selection effects. However, even when taking selection effects into account, we still find a relation between M/L evolution and mass, which is most likely caused by a lower mean age and a larger intrinsic scatter for low mass galaxies. Results from lensing early-type galaxies, which are mass-selected, show a very similar trend with mass. This, combined with our findings, provides evidence for down-sizing. Previous studies of the rate of evolution of field early-type galaxies found a large range of mutually exclusive values. We show that these differences are largely caused by the differences between fitting methods. (Abridged)Comment: figures 3 and 4 available at http://www.strw.leidenuniv.nl/~vdwel/private/FPpaper

Infall, the Butcher-Oemler Effect, and the Descendants of Blue Cluster Galaxies at z~0.6

Using wide-field HST/WFPC2 imaging and extensive Keck/LRIS spectroscopy, we present a detailed study of the galaxy populations in MS2053--04, a massive, X-ray luminous cluster at z=0.5866. Analysis of 149 confirmed cluster members shows that MS2053 is composed of two structures that are gravitationally bound to each other; their respective velocity dispersions are 865 km/s (113 members) and 282 km/s (36 members). MS2053's total dynamical mass is 1.2x10^15 Msun. MS2053 is a classic Butcher-Oemler cluster with a high fraction of blue members (24%) and an even higher fraction of star-forming members (44%), as determined from their [OII] emission. The number fraction of blue/star-forming galaxies is much higher in the infalling structure than in the main cluster. This result is the most direct evidence to date that the Butcher-Oemler effect is linked to galaxy infall. In terms of their colors, luminosities, estimated internal velocity dispersions, and [OII] equivalent widths, the infalling galaxies are indistinguishable from the field population. MS2053's deficit of S0 galaxies combined with its overabundance of blue spirals implies that many of these late-types will evolve into S0 members. The properties of the blue cluster members in both the main cluster and infalling structure indicate they will evolve into low mass, L<L* galaxies with extended star formation histories like that of low mass S0's in Coma. Our observations show that most of MS2053's blue cluster members, and ultimately most of its low mass S0's, originate in the field. Finally, we measure the redshift of the giant arc in MS2053 to be z=3.1462; this object is one in only a small set of known strongly lensed galaxies at z>3.Comment: Accepted by ApJ. Version with full resolution figures available at http://www.exp-astro.phys.ethz.ch/tran/outgoing/ms2053.ps.g

Micro-Jy radio sources in the z=0.83 cluster MS1054-03

An extremely deep 5 GHz radio observation is presented of the rich cluster MS1054-03 at redshift z=0.83. 34 radio sources are detected down to a 32 micro-Jy (6 sigma), compared to about 25 expected from previous blank field radio source count determinations; the sources giving rise to these excess counts lie within 2 arcmins (700 kpc) of the cluster centre. Existing imaging and spectroscopy has provided optical identifications for 21 of the radio sources and redshifts for 11, of which 8 are confirmed cluster members. 4 of these 8 confirmed cluster sources are associated with close galaxy pairs (10-25 kpc projected offset) of similar magnitude, implying that the radio source may be triggered by an interaction. However, although MS1054-03 has a very high fraction (17%) of on-going mergers (separations <~ 10 kpc), no radio emission is detected towards any of these merger events, setting a mean upper limit of 10 Msun/yr for any star formation associated with these mergers. This supports a hypothesis that low luminosity radio sources may be onset by initial weak interactions rather than direct mergers. The host galaxies of the other four confirmed cluster radio sources are all isolated, and show a range of morphologies from early-type to Sc. A comparison between the emission line and radio luminosities suggests that two of these four radio sources are low-luminosity AGN, whilst for at least one of the other two the radio emission is associated with on-going star formation. All of the radio sources associated with the galaxy pairs appear more likely AGN than starburst origin. The overall proportion of radio sources associated with AGN in this cluster (>75%) is higher than at these flux density levels in the field (40-50%).Comment: 19 pages LaTeX, including 8 figures. Accepted for publication in MNRAS. Version with higher resolution figures available from http://www.roe.ac.uk/~pnb/papers.htm

The Fundamental Plane at z=1.27: First Calibration of the Mass Scale of Red Galaxies at Redshifts z>1

We present results on the Fundamental Plane (FP) of early-type galaxies in the cluster RDCS J0848+4453 at z=1.27. Internal velocity dispersions of three K-selected early-type galaxies are determined from deep Keck spectra. Structural parameters are determined from HST NICMOS images. The galaxies show substantial offsets from the FP of the nearby Coma cluster, as expected from passive evolution of their stellar populations. The offsets from the FP can be expressed as offsets in M/L ratio. The M/L ratios of the two most massive galaxies are consistent with an extrapolation of results obtained at z=0.02-0.83. The evolution of early-type galaxies with masses >10^11 M_sun is well described by ln M/L(B) = (-1.06 +- 0.09) z, corresponding to passive evolution of -1.50 +- 0.13 mag at z=1.3. Ignoring selection effects, the best fitting stellar formation redshift is z*=2.6, corresponding to a luminosity weighted age at the epoch of observation of ~2 Gyr. The M/L ratios of these two galaxies are also in excellent agreement with predictions from models that include progenitor bias. The third galaxy is a factor ~10 less massive than the other two, shows strong Balmer absorption lines in its spectrum, and is offset from the Coma Fundamental Plane by 2.9 mag in rest-frame B. Despite their large range in M/L ratios, all three galaxies fall in the ``Extremely Red Object'' (ERO) class with I-H>3 and R-K>5, and our results show that it is hazardous to use simple models for converting luminosity to mass for these objects. Measurements of M/L ratios at high redshift can be considered first steps to empirically disentangle luminosity and mass evolution at the high mass end of the galaxy population, lifting an important degeneracy in the interpretation of evolution of the luminosity function. [SHORTENED]Comment: Accepted for publication in the Astrophysical Journa

The Fundamental Plane of Field Early Type Galaxies at z=1

We present deep VLT spectra of early type galaxies at z~1 in the Chandra Deep Field South, from which we derive velocity dispersions. Together with structural parameters from Hubble Space Telescope imaging, we can study the Fundamental Plane for field early type galaxies at that epoch. We determine accurate mass-to-light ratios and colors for four field early type galaxies in the redshift range 0.96<z<1.14, and two with 0.65<z<0.70. The galaxies were selected by color and morphology, and have generally red colors. Their velocity dispersions show, however, that they have a considerable spread in mass-to-light ratios (factor of 3). We find that the colors and directly measured mass-to-light ratios correlate well, demonstrating that the spread in mass-to-light ratios is real and reflects variations in stellar populations. The most massive galaxies have mass-to-light ratios comparable to massive cluster galaxies at similar redshift, and therefore have stellar populations which formed at high redshift (z>2). The lower mass galaxies at z~1 have a lower average mass-to-light ratio, and one is a genuine 'E+A' galaxy. The mass-to-light ratios indicate that their luminosity weighted ages are a factor of three younger at the epoch of observation, due to either a late formation redshift, or due to late bursts of star formation contributing 20-30% of the mass.Comment: 4 pages incl. 4 figures, Accepted for publication in ApJ Letter

Spectroscopic Confirmation of Multiple Red Galaxy-Galaxy Mergers in MS1054-03 (z=0.83)

We present follow-up spectroscopy of the galaxy cluster MS1054-03 (z=0.83) confirming that at least six of the nine merging galaxy pairs identified by van Dokkum et al. (1999) are indeed bound systems: they have projected separations of R_s<10 kpc and relative line-of sight velocities of dv<165 km/s. For the remaining three pairs, we were unable to obtain redshifts of both constituent galaxies. To identify a more objective sample of merging systems, we select bound red galaxy pairs (R_s<=30 kpc, dv<=300 km/s) from our sample of 121 confirmed cluster members: galaxies in bound red pairs make up 15.7+/-3.6% of the cluster population. The (B-K_s) color-magnitude diagram shows that the pair galaxies are as red as the E/S0 members and have a homogeneous stellar population. The red pair galaxies span a large range in luminosity and internal velocity dispersion to include some of the brightest, most massive members (L>L*, sigma>200 km/s); these bound galaxy pairs must evolve into E/S0 members by z~0.7. These results combined with MS1054's high merger fraction and reservoir of likely future mergers indicates that most, if not all, of its early-type members evolved from (passive) galaxy-galaxy mergers at z<~1.Comment: accepted by ApJ Letters; high resolution version of Fig. 2 available at http://www.exp-astro.phys.ethz.ch/tran/outgoing/ms1054mgrs.ps.g

Hubble Space Telescope weak lensing study of the z=0.83 cluster MS 1054-03

We have measured the weak gravitational lensing signal of MS 1054-03, a rich and X-ray luminous cluster of galaxies at a redshift of z=0.83, using a two-colour mosaic of deep WFPC2 images. The small corrections for the size of the PSF and the high number density of background galaxies obtained in these observations result in an accurate and well calibrated measurement of the lensing induced distortion. The strength of the lensing signal depends on the redshift distribution of the background galaxies. We used photometric redshift distributions from the Northern and Southern Hubble Deep Fields to relate the lensing signal to the mass. The predicted variations of the signal as a function of apparent source magnitude and colour agrees well with the observed lensing signal. We determine a mass of (1.2+-0.2)x10^15 Msun within an aperture of radius 1 Mpc. Under the assumption of an isothermal mass distribution, the corresponding velocity dispersion is 1311^{+83}_{-89} km/s. For the mass-to-light ratio we find 269+-37 Msun/Lsun. The errors in the mass and mass-to-light ratio include the contribution from the random intrinsic ellipticities of the source galaxies, but not the (systematic) error due to the uncertainty in the redshift distribution. However, the estimates for the mass and mass-to-light ratio of MS 1054-03 agree well with other estimators, suggesting that the mass calibration works well. The reconstruction of the projected mass surface density shows a complex mass distribution, consistent with the light distribution. The results indicate that MS 1054-03 is a young system. The timescale for relaxation is estimated to be at least 1 Gyr. Averaging the tangential shear around the cluster galaxies, we find that the velocity dispersion of an Lstar galaxy is 203+-33 km/s.Comment: 21 pages, Latex, with 27 figures (3 figures bitmapped), ApJ, in press. Version (with non-bitmapped figures) available at http://www.astro.rug.nl/~hoekstra/papers.htm

Assessing HeartSong as a Neonatal Music Therapy Intervention:A Qualitative Study on Personal and Professional Caregivers' Perspectives

Background: The music therapy HeartSong intervention pairs newborn infant heartbeats with parents' Song of Kin. Formal evidence on professional and personal caregiver perspectives of this intervention is lacking. Purpose: This survey study evaluates the HeartSong music therapy intervention from parent and staff perspectives. Methods: A qualitative study assessing inclusion of HeartSong for family neonatal intensive care unit (NICU) care surveyed 10 professional caregivers comprising medical and psychosocial NICU teams anonymously reflecting their impressions of the intervention. Digital survey of parents/guardians contacted through semistructured phone interviews relayed impressions of recordings: subsequent setup, Song of Kin selection, and use of HeartSong, including thoughts/feelings about it as an intervention. Results: Professional and personal caregivers valued the HeartSong intervention for bereavement support, family support, including parental, extended family/infant support, and to enhance bonding. Emergent themes: memory-making, connectedness/closeness, support of parent role, processing mental health needs of stressful NICU days, and subsequent plans for lifelong HeartSong use. Therapeutic experience was named as a crucial intervention aspect and participants recommended the HeartSong as a viable, accessible NICU intervention. Implications for Practice and Research: HeartSong's use showed efficacy as a clinical NICU music therapy intervention for families of critically ill and extremely preterm infants, when provided by trained, specialized, board-certified music therapists. Future research focusing on HeartSong in other NICU populations might benefit infants with cardiac disease, parental stress, and anxiety attending to parent-infant bonding. Costs and time benefits related to investment are needed before implementation is considered.</p