The Assembly History of Field Spheroidals: Evolution of Mass-to-light Ratios and Signatures of Recent Star Formation

Details The Assembly History of Field Spheroidals: Evolution of Mass-to-light Ratios and Signatures of Recent Star Formation The Assembly History of Field Spheroidals: Evolution of Mass-to-light Ratios and Signatures of Recent Star Formation

2005-03-07

arxiv.org/abs/astro-ph/0503164v1

Astrophys.J.633:174-197,2005

Astronomy and Astrophysics

Astrophysics

26 pages including 24 figures, submitted to ApJ. Complete and compact version with full resolution images available at http:

Scientific paper

10.1086/444585

We present a comprehensive catalog of high signal-to-noise spectra obtained with the DEIMOS spectrograph on the Keck II telescope for a sample of F850LP<22.43 (AB) field spheroidal (E+S0s; 163) and bulge dominated disk (61) galaxies in the redshift range 0.2=-0.72^{+0.07}_{-0.05}\pm0.04. However, this evolution depends significantly on the dynamical mass, being slower for larger masses as reported in a previous letter. In addition, we separately show the intrinsic scatter of the FP increases with redshift as d(rms(M/L_{\rm B}))/dz=0.040\pm0.015. Although these trends are consistent with single burst populations which formed at $z_f>2$ for high mass spheroidals and z_{f}~1.2 for lower mass systems, a more realistic picture is that most of the stellar mass formed in all systems at z>2 with subsequent activity continuing to lower redshifts (z<1.2). The fraction of stellar mass formed at recent times depend strongly on galactic mass, ranging from <1% for masses above 10^{11.5} M_{\odot} to 20-40% below 10^{11} M_{\odot}. Independent support for recent activity is provided by spectroscopic ([\ion{O}{2}] emission, H\delta) and photometric (blue cores and broad-band colors) diagnostics. Via the analysis of a large sample with many independent diagnostics, we are able to reconcile previously disparate interpretations of the assembly history of field spheroidals. [Abridged]

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