Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies

Abstract

The relation between X‐ray luminosity and near‐infrared (NIR) luminosity for early‐type galaxies has been examined. NIR luminosities should provide a superior measure of stellar mass compared to optical luminosities used in previous studies, especially if there is significant star formation or dust present in the galaxies. However, we show that the X‐ray–NIR relations are remarkably consistent with the X‐ray–optical relations. This indicates that the large scatter of the relations is dominated by scatter in the X‐ray properties of early‐type galaxies, and is consistent with early‐types consisting of old, quiescent stellar populations. We have investigated scatter in terms of environment, surface brightness profile, Mg2, Hβ, Hγ line strength indices, spectroscopic age and nuclear Hα emission. We found that galaxies with high Mg2 index, low Hβ and Hγ indices or a ‘core’ profile have a large scatter in LX, whereas galaxies with low Mg2, high Hβ and Hγ indices or ‘power‐law’ profiles generally have LX < 1041 erg s−1. There is no clear trend in the scatter with environment or nuclear Hα emission.

SPECTRAL ENERGY DISTRIBUTION MAPPING OF TWO ELLIPTICAL GALAXIES ON SUB-kpc SCALES

“…Hot, warm and cold gas detections have been reported by several authors (eg. Caon et al 2000;Mathews & Brighenti 2003;Sarzi et al 2006Sarzi et al , 2013Mulchaey & Jeltema 2010;Ellis & O'Sullivan 2006;Davis et al 2011;Serra et al 2012) The cold ISM is often spatially extended, with irregular distribution and kinematics (Caon et al 2000). Dust is also present in all the phases of the ISM (Temi et al 2005(Temi et al , 2009Smith et al 2012), and the dust-to-gas ratio can be used to track down the origin of the cold gas.…”

Scaling properties of the hot gas in early-type galaxies

“…However, Ellis & O'Sullivan (2006) showed that replacing LB by K-band luminosity in Fig.1, results in a very similar scatter.…”

“…Galaxy environment - Ellis & O'Sullivan (2006) found no clear environmental trend in LX /LB , apart from the high values apparent in BGGs and BCGs. However, recent studies with Chandra, which is better able to resolve galaxy emission, show that LX /LB is suppressed by a factor ∼3-4 in non-central galaxies within both clusters (Sun et al (2007)) and groups (Jeltema et al (2008)).…”

“…This is consistent with the earlier result, that 292 T. J. Ponman & E. J. O'Sullivan Figure 1. LX -LB plot for 401 early-type galaxies from Ellis & O'Sullivan (2006). The long dashed line is the discrete source contribution estimated by Kim & Fabbiano (2004), other lines show fits to various subsets of the sample, and the grey diamonds represent the mean LX in a series of LB bins.…”

“…X-ray data quality -The X-ray data used by Ellis & O'Sullivan (2006) came from ROSAT. However, smaller samples of higher quality datasets from Chandra and XMM (e.g.…”