The Evolution of Balmer Absorption Line Strengths in E/S0 Galaxies from z=0 to z=0.83

We use new models of stellar population synthesis to estimate the fraction of stars formed during the last major bursts of star formation in E/S0 galaxies in low-redshift clusters ($z\simlt0.4$) from the spectral signatures of intermediate-age stars. We find that the mass fraction of stars formed in late bursts in early-type galaxies in clusters must have decreased smoothly with redshift, from about 8\% at $z\approx1$ to less than 1\% at $z\approx0$. This result, which we int...

We discuss the galaxy population of the rich cluster MS1621.5+2640 at z=0.4274, based on spectra and imaging in a field of size 9 arcmin by 23 arcmin (~2 by 5 h**-1 Mpc). The sample comprises 277 galaxies, of which 112 are cluster members, 7 are `near-members', and 47 are field galaxies in the redshift range 0.37<=z<=0.50. The results are analyzed and compared with the z=0.2279 rich cluster Abell 2390. MS1621.5+2640 has a higher blue fraction, a younger stellar population, an...

The IMACS Cluster Building Survey (ICBS) provides spectra of ~2200 galaxies 0.31<z<0.54 in 5 rich clusters (R <= 5 Mpc) and the field. Infalling, dynamically cold groups with tens of members account for approximately half of the supercluster population, contributing to a growth in cluster mass of ~100% by today. The ICBS spectra distinguish non-starforming (PAS) and poststarburst (PSB) from starforming galaxies -- continuously starforming (CSF) or starbursts, (SBH or SBO), id...

One important approach to the study of galaxy evolution is to identify those galaxies whose spectral and/or morphological characteristics suggest that they are in transition. For example, ``E+A'' galaxies, which have strong Balmer absorption lines and no significant [OII] emission, are generally interpreted as post-starburst galaxies in which the star formation ceased within the last Gyr. This transition between a star forming and non-star forming state is a critical link in ...

We report results from a panoramic spectroscopic survey of 955 objects in the field of the rich cluster Cl 0024+1654 (z~0.4), complementing the HST imaging presented in the first paper in this series. Our new spectroscopic sample includes over 200 high quality spectra of cluster members, spread across an area 10 Mpc in diameter. We examine the properties of a large sample of 104 cluster early-types as a function of cluster radius and local density, using them as sensitive tra...

We use integral field spectroscopy from the SAMI Galaxy Survey to identify galaxies that show evidence for recent quenching of star formation. The galaxies exhibit strong Balmer absorption in the absence of ongoing star formation in more than 10% of their spectra within the SAMI field of view. These $\rm{H}{\delta}$-strong galaxies (HDSGs) are rare, making up only $\sim 2$% (25/1220) of galaxies with stellar mass ${\rm log(}M_*/M_{\odot})>10$. The HDSGs make up a significant ...

About 35 years ago a class of galaxies with unusually strong Balmer absorption lines and weak emission lines was discovered in distant galaxy clusters. These objects, alternatively referred to as post-starburst, E+A or k+a galaxies, are now known to occur in all environments and at all redshifts, with many exhibiting compact morphologies and low-surface brightness features indicative of past galaxy mergers. They are commonly thought to represent galaxies that are transitionin...

We present a new method to estimate the average star formation rate per unit stellar mass (SSFR) of a stacked population of galaxies. We combine the spectra of 600-1000 galaxies with similar stellar masses and parameterise the star formation history of this stacked population using a set of exponentially declining functions. The strength of the Hydrogen Balmer absorption line series in the rest-frame wavelength range 3750-4150\AA is used to constrain the SSFR by comparing wit...

We present a detailed analysis of the spectroscopic catalog of galaxies in 10 distant clusters from Dressler et al. (1999, D99). We investigate the nature of the different spectral classes defined by D99 including star forming, post-starburst and passive galaxy populations, and reproduce their basic properties using our spectral synthesis model. We attempt to identify the evolutionary pathways between the various spectral classes in order to search for the progenitors of the ...

E+A galaxies are characterized as a galaxy with strong Balmer absorption lines but without any [OII] or Halpha emission lines. Strong Balmer absorption lines indicate that E+A galaxies have experienced a starburst within the last <1-1.5 Gyr. However, the lack of emission lines indicates that E+A galaxies do not have any on-going star formation. Therefore, E+A galaxies are interpreted as a post-starburst galaxy. However, it has been a mystery why E+A galaxies underwent a starb...