Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRXJ0848.6+4453: The Evolution of Galaxy Sizes and Stellar Populations in a z=1.27 Cluster
99
0
0.0
(
0
)
Authors
Inger Jorgensen
Ask ChatGPT about the research
No Arabic abstract
RXJ0848.6+4453 (Lynx W) at redshift 1.27 is part of the Lynx Supercluster of galaxies. Our analysis of stellar populations and star formation history in the cluster covers 24 members and is based on deep optical spectroscopy from Gemini North and imaging data from HST. Focusing on the 13 bulge-dominated galaxies for which we can determine central velocity dispersions, we find that these show a smaller evolution of sizes and velocity dispersions than reported for field galaxies and galaxies in poorer clusters. The galaxies in RXJ0848.6+4453 populate the Fundamental Plane similar to that found for lower redshift clusters with a zero point offset corresponding to an epoch of last star formation at z_form= 1.95+-0.2. The spectra of the galaxies in RXJ0848.6+4453 are dominated by young stellar populations at all galaxy masses and in many cases show emission indicating low level on-going star formation. The average age of the young stellar populations (estimated from H-zeta) is consistent with a major star formation episode 1-2 Gyr prior, which in turn agrees with z_form=1.95. Galaxies dominated by young stellar populations are distributed throughout the cluster. We speculate that low level star formation has not yet been fully quenched in the center of this cluster may be because the cluster is significantly poorer than other clusters previously studied at similar redshifts, which appear to have very little on-going star formation in their centers.
rate research
Read More
We present detailed, high spatial and spectral resolution, long-slit observations of four central cluster galaxies (Abell 0085, 0133, 0644 and Ophiuchus) recently obtained on the Southern African Large Telescope (SALT). Our sample consists of central cluster galaxies (CCGs) with previously-observed Halpha-filaments, and have existing data from the X-ray to radio wavelength regimes available. Here, we present the detailed optical data over a broad wavelength range to probe the spatially-resolved kinematics and stellar populations of the stars. We use the Pegase.HR model with the ELODIE v3.1 stellar library to determine the star formation histories of the galaxies using full spectrum fitting. We perform single stellar population (SSP) as well as composite stellar population (CSP) fits to account for more complex star formation histories. Monte-Carlo simulations and chi 2-maps are used to check the reliability of the solutions. This, combined with the other multiwavelength data, will form a complete view of the different phases (hot and cold gas and stars) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters, as well as the influence of the host cluster. We find small, young stellar components in at least three of the four galaxies, even though two of the three host clusters have zero spectrally-derived mass deposition rates from X-ray observations.
We study the stellar population far into the halo of one of the two brightest galaxies in the Coma cluster, NGC 4889, based on deep medium resolution spectroscopy with FOCAS at the Subaru 8.2m telescope. We fit single stellar population models to the measured line-strength (Lick) indices (Hbeta, Mgb, [MgFe] and <Fe>). Combining with literature data, we construct radial profiles of metallicity, [alpha/Fe] element abundance ratio and age for NGC 4889, from the center out to ~60 kpc (~4Re). We find evidence for different chemical and star formation histories for stars inside and outside 1.2Re = 18 kpc radius. The inner regions are characterized by a steep [Z/H] gradient and high [alpha/Fe] at ~2.5 times solar value. In the halo, between 18 and 60 kpc, the [Z/H] is near-solar with a shallow gradient, while [alpha/Fe] shows a strong negative gradient, reaching solar values at ~60 kpc. We interpret these data in terms of different formation histories for both components. The data for the inner galaxy are consistent with a rapid, quasi-monolithic, dissipative merger origin at early redshifts, followed by one or at most a few dry mergers. Those for the halo argue for later accretion of stars from old systems with more extended star formation histories. The half-light radius of the inner component alone is estimated as ~6 kpc, suggesting a significantly smaller size of this galaxy in the past. This may be the local stellar population signature of the size evolution found for early-type galaxies from high-redshift observations.
We present B and V time-series photometry of Andromeda XXV, the third galaxy in our program on the Andromedas satellites, that we have imaged with the Large Binocular Cameras of the Large Binocular Telescope. The field of Andromeda XXV is found to contain 63 variable stars, for which we present light curves and characteristics of the light variation (period, amplitudes, variability type, mean magnitudes, etc.). The sample includes 58 RR Lyrae variables (46 fundamental-mode $-$ RRab, and 12 first-overtone $-$RRc, pulsators), three anomalous Cepheids, one eclipsing binary system and one unclassified variable. The average period of the RRab stars ($langle Pab rangle$ = 0.60 $sigma=0.04$ days) and the period-amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects. From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of (m-M)$_0$=$24.63pm0.17$ mag. The color-magnitude diagram reveals the presence in Andromeda XXV of a single, metal-poor ([Fe/H]=$-$1.8 dex) stellar population as old as $sim$ 10-12 Gyr traced by a conspicuous red giant branch and the large population of RR Lyrae stars. We discovered a spherically-shaped high density of stars near the galaxy center. This structure appears to be at a distance consistent with Andromeda XXV and we suggest it could either be a star cluster or the nucleus of Andromeda XXV. We provide a summary and compare number and characteristics of the pulsating stars in the M31 satellites analyzed so far for variability.
We compute optical galaxy luminosity functions (GLFs) in the B, V, R, and I rest-frame bands for one of the largest medium-to-high-redshift (0.4 < z < 0.9) cluster samples to date in order to probe the abundance of faint galaxies in clusters. We also study how the GLFs depend on cluster redshift, mass, and substructure, and compare the GLFs of clusters with those of the field. We separately investigate the GLFs of blue and red-sequence (RS) galaxies to understand the evolution of different cluster populations. We find that the shapes of our GLFs are similar for the B, V, R, and I bands with a drop at the red GLF faint end that is more pronounced at high-redshift: alpha(red) ~ -0.5 at 0.40 < z < 0.65 and alpha(red) > 0.1 at 0.65 < z < 0.90. The blue GLFs have a steeper faint end (alpha(blue) ~ -1.6) than the red GLFs, that appears to be independent of redshift. For the full cluster sample, blue and red GLFs intersect at M(V) = -20, M(R) = -20.5, and M(I) = -20.3. A study of how galaxy types evolve with redshift shows that late type galaxies appear to become early types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of more massive clusters appear to be richer than less massive clusters, which is more typical of the lower redshift behaviour. Our results indicate that our clusters form at redshifts higher than z = 0.9 from galaxy structures that already have an established red sequence. Late type galaxies then appear to evolve into early types, enriching the red-sequence between this redshift and today. This effect is consistent with the evolution of the faint end slope of the red-sequence and the galaxy type evolution that we find. Finally, faint galaxies accreted from the field environment at all redshifts might have replaced the blue late type galaxies that converted into early types, explaining the lack of evolution in the faint end slopes of the blue GLFs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
