Galaxy formation and evolution

Abstract:

Black hole (BH) masses predicted from the Ṁ-σ relationship conflict with predictions from the Ṁ-L relationship for high-luminosity galaxies, such as brightest cluster galaxies (BCGs). The Ṁ-L relationship predicts that some BCGs may harbor BHs with M approaching 1010 M⊙, while the Ṁ- σ relationship always predicts Ṁ < 3 × 10 9 M⊙. We argue that the Ṁ-L relationship is a plausible description for galaxies of high luminosity. If the cores in central stellar density are formed by binary BHs, the inner core cusp radius, rγ, may be an independent witness of Ṁ. Using central structural parameters derived from a large sample of early-type galaxies observed by HST, we argue that L is superior to σ as an indicator of rγ. Further, the rγ-Ṁ relationship for 11 core galaxies with measured Ṁ appears to be consistent with the Ṁ-L relationship for BCGs. BCGs have large cores appropriate for their large luminosities that may be difficult to generate with the more modest BH masses inferred from the Ṁ-σ relationship. Ṁ ∼ M would be expected for BCGs, if they were formed in dissipationless mergers, which should preserve the ratio of BH to stellar mass, M. This scenario appears to be consistent with the slow increase in a with L and the more rapid increase in effective radii with L seen in BCGs as compared to less luminous galaxies. If BCGs have large BHs commensurate with their luminosities, then the local BH mass function for Ṁ > 3 × 109 M⊙ ould be nearly an order of magnitude richer than that inferred from the Ṁ-σ relationship. The volume density of the most luminous QSOs may favor the Ṁ-L relationship. © 2007. The American Astronomical Society. All rights reserved.

Abstract:

We present the results of an optical and near-IR spectroscopic study of giant nebular emission-line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07, and B2 0902+34. Previous deep narrowband Lyα imaging revealed complex morphologies with sizes up to 100 kpc, possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km s-1 and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions > 1000 km ss-:. The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of ≈60 kpc along the radio axis. The dynamical structures traced in the Lyα line are, in most cases, closely echoed in the carbon and oxygen lines. This shows that the Lyα line is produced in a highly clumped medium of small filling factor and can therefore be used as a tracer of the dynamics of high-redshift radio galaxies (HzRGs). We conclude that these HzRGs are under-going a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming "red and dead" elliptical galaxies. © 2007, The American Astronomical Society. All rights reserved.

Abstract:

We study 87 extremely red objects (EROs), selected both to have color redder than R - [3.6] = 4.0 and to have confirmed spectroscopic redshifts. Together, these two constraints result in this sample populating a fairly narrow redshift range at 0.76 < z < 1.42. The key new ingredient included here is deep Spitzer Space Telescope Infrared Array Camera (IRAC) data. Based on [3.6] - [8.0] color, we demonstrate that it is possible to classify EROs as early-type galaxies, dusty starburst galaxies, or active galactic nuclei (AGNs; power-law types). We present ultraviolet-to-mid-infrared spectral energy distributions (SEDs) and Advanced Camera for Surveys (ACS) images, both of which support our simple IRAC color classification. © 2007. The American Astronomical Society. All rights reserved.

Abstract:

We report the detection of rest-frame 6.2 and 7.7 μm emission features arising from polycyclic aromatic hydrocarbons (PAHs) in the Spitzer IRS spectrum of an infrared-luminous Lyman break galaxy at z = 3.01. This is currently the highest redshift galaxy where these PAH emission features have been detected. The total IR luminosity inferred from the MIPS 24 μm and radio flux density is 2 × 1013 L⊙, which qualifies this object as a so-called hyperluminous infrared galaxy (HyLIRG). However, unlike local HyLIRGs, which are generally associated with QSO/AGNs and have weak or absent PAH emission features, this HyLIRG has very strong 6.2 and 7.7 μm PAH emission. We argue that intense star formation dominates the IR emission of this source, although we cannot rule out the presence of a deeply obscured AGN. This LBG appears to be a distorted system in the HST ACS F606W and F814W images, possibly indicating that a significant merger or interaction is driving the large IR luminosity. © 2007. The American Astronomical Society. All rights reserved.