The Origin of Blue Cores in Hubble Deep Field E/S0 Galaxies

Abstract

In this Letter we address the problem of the origin of blue cores and inverse color gradients in early-type galaxies reported in the Hubble Deep Field-North and Hubble Deep Field-South by Menanteau, Abraham, & Ellis. We use a multizone single-collapse model. This model accounts for the observed blue cores by adopting a broad spread in formation redshifts for elliptical galaxies, allowing some of these galaxies to begin forming no more than ∼1 Gyr before the redshift of observation. The single-zone collapse model then produces cores that are bluer than the outer regions because of the increase of the local potential well toward the center, which makes star formation more extended in the central region of the galaxy. We compare the predicted V 606 ϪI 814 (r) color gradients with those observed using the redshift of formation ( ) of the elliptical as the only free parameter.z F We find that the model can account with relatively good agreement for the blue cores and inverse color gradients found in many spheroidals and at the same time for the red and smooth color profiles reported. Based on the model, our analysis suggests two populations of field elliptical galaxies, one formed recently, within Շ1 Gyr, and another much older, formed տ4 Gyr since the redshift of observation.

SNe heating and the chemical evolution of the intra-cluster medium

“…We assume galaxies to have formed 13 Gyr ago corresponding to a formation redshift z f = 8.0 for the adopted cosmology. It is worth noting that all of the models described here reproduce the main features of elliptical galaxies, such as the present time type Ia SN rate, the metallicity of the dominant stellar population and the color-magnitude diagram, as already discussed in previous papers where we address the reader for details (Matteucci and Gibson, 1995;Matteucci, Ponzone & Gibson 1998;Martinelli, Matteucci & Colafrancesco, 1998;Menanteau et al 2001). Here we discuss only the evolution of the abundances and energetic content of the ICM.…”

“…The distribution of the dark matter is assumed to be the same as in the one-zone model, whereas the distribution of luminous matter follows that of Jaffe (1983). This kind of multizone model well reproduces both abundance (Martinelli et al 1998) and color (Menanteau et al 2001) gradients inside ellipticals.…”

The Host Galaxies and Environment of Chandra ‐Selected Active Galactic Nuclei in the Deep ACS GTO Cluster Fields

“…Before the advent of ACS, they had been detected only in extremely deep broadband HST WFPC2 observations (e.g., the HDFs) and deep spectroscopic observations have been rather limited due to the long integration times required to acquire a high-signal spectrum. Blue cores in early types have traditionally been associated with star formation attributed to differences in the local potential well in the galaxies' central regions ( Menanteau et al 2001b;Friaça & Terlevich 2001). But recently, some blue core early types have been associated with luminous X-ray sources, suggesting that at least in these objects, the nonthermal emission from the central AGN may contribute significantly to the observed central color gradients ( Menanteau et al 2005a( Menanteau et al , 2005bTreu et al 2005).…”

X-ray-emitting active galactic nuclei fromz= 0.6 to 1.3 in the intermediate- and high-density environments of the ORELSE survey

“…One such mechanism is major galaxy mergers, which can create inflows of gas to galactic nuclei, fueling bulge growth and an AGN (Hopkins et al 2006;Narayanan et al 2008). Many others have been proposed, as well, including minor mergers or tidal interactions (Moore et al 1996;Menanteau, Jimenez & Matteucci 2001;Younger et al 2008;Georgakakis et al 2009), processes such as disk or bar instabilities or turbulence (Elmegreen et al 1998;Genzel et al 2008;Younger et al 2008;Hopkins & Quataert 2010;Bournaud et al 2011), and recycling of stellar material (Ciotti & Ostriker 2007).…”