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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/24389
Title: Hidden Active Galactic Nuclei in Early-type Galaxies
Authors: PAGGI, Alessandro 
Fabbiano, Giuseppina
Civano, Francesca
Pellegrini, Silvia
Elvis, Martin
Kim, Dong-Woo
Issue Date: 2016
Journal: THE ASTROPHYSICAL JOURNAL 
Number: 823
Issue: 2
First Page: 112
Abstract: We present a stacking analysis of the complete sample of early-type galaxies (ETGs) in the Chandra COSMOS (C-COSMOS) survey, to explore the nature of the X-ray luminosity in the redshift and stellar luminosity ranges 0\lt z\lt 1.5 and {10}<SUP>9</SUP>\lt {L}<SUB>K</SUB>/{L}<SUB>☉ </SUB>\lt {10}<SUP>13</SUP>. Using established scaling relations, we subtract the contribution of X-ray binary populations to estimate the combined emission of hot ISM and active galactic nuclei (AGNs). To discriminate between the relative importance of these two components, we (1) compare our results with the relation observed in the local universe {L}<SUB>X,{gas</SUB>}\propto {L}<SUB>K</SUB><SUP>4.5</SUP> for hot gaseous halos emission in ETGs, and (2) evaluate the spectral signature of each stacked bin. We find two regimes where the non-stellar X-ray emission is hard, consistent with AGN emission. First, there is evidence of hard, absorbed X-ray emission in stacked bins including relatively high z (∼1.2) ETGs with average high X-ray luminosity ({L}<SUB>X {-</SUB> {LMXB}}≳ 6× {10}<SUP>42</SUP> {{erg}} {{{s}}}<SUP>-1</SUP>). These luminosities are consistent with the presence of highly absorbed “hidden” AGNs in these ETGs, which are not visible in their optical-IR spectra and spectral energy distributions. Second, confirming the early indication from our C-COSMOS study of X-ray detected ETGs, we find significantly enhanced X-ray luminosity in lower stellar mass ETGs ({L}<SUB>K</SUB>≲ {10}<SUP>11</SUP>{L}<SUB>☉ </SUB>), relative to the local {L}<SUB>X,{gas</SUB>}\propto {L}<SUB>K</SUB><SUP>4.5</SUP> relation. The stacked spectra of these ETGs also suggest X-ray emission harder than expected from gaseous hot halos. This emission is consistent with inefficient accretion {10}<SUP>-5</SUP>-{10}<SUP>-4</SUP>{\dot{M}}<SUB>{Edd</SUB>} onto {M}<SUB>{BH</SUB>}∼ {10}<SUP>6</SUP>-{10}<SUP>8</SUP> {M}<SUB>☉ </SUB>.
URI: http://hdl.handle.net/20.500.12386/24389
URL: https://iopscience.iop.org/article/10.3847/0004-637X/823/2/112
ISSN: 0004-637X
DOI: 10.3847/0004-637X/823/2/112
Bibcode ADS: 2016ApJ...823..112P
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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