AMUSE-Field I: Nuclear X-ray Properties of Local Field and Group Spheroids across the Stellar Mass Scale

📝 Abstract

We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occurrence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance-limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3-10 keV) luminosity of 2.5x10^38 erg/s, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45+/-7 percent, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with -8<log(L_X/L_Edd)<-4. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of “Eddington incompleteness” within the lower-mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M_star^(0.71+/-0.10), with an intrinsic scatter of 0.73+/-0.09 dex. A majority of the AMUSE-Field galaxies (78%) inhabits groups, enabling us to investigate the influence of group richness upon nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for isolated galaxies, and that this trend continues to cluster early-types.

💡 Analysis

We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occurrence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance-limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3-10 keV) luminosity of 2.5x10^38 erg/s, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45+/-7 percent, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with -8<log(L_X/L_Edd)<-4. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of “Eddington incompleteness” within the lower-mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M_star^(0.71+/-0.10), with an intrinsic scatter of 0.73+/-0.09 dex. A majority of the AMUSE-Field galaxies (78%) inhabits groups, enabling us to investigate the influence of group richness upon nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for isolated galaxies, and that this trend continues to cluster early-types.

📄 Content

arXiv:1112.3985v2 [astro-ph.HE] 13 Jan 2012 Draft version November 6, 2018 Preprint typeset using LATEX style emulateapj v. 12/16/11 AMUSE-FIELD I: NUCLEAR X-RAY PROPERTIES OF LOCAL FIELD AND GROUP SPHEROIDS ACROSS THE STELLAR MASS SCALE Brendan Miller,1 Elena Gallo,1 Tommaso Treu,2 and Jong-Hak Woo3 Draft version November 6, 2018 ABSTRACT We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occur- rence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance- limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3–10 keV) luminosity of 2.5 × 1038 erg s−1, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45 ± 7%, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with LX/LEdd ratios between ∼10−4– 10−8. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of “Eddington incompleteness” within the lower- mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M 0.71±0.10 star , with an intrinsic scatter of 0.73 ± 0.09 dex. Qualitatively similar results hold for morphologically homogeneous (type E) or uniform sensitivity (new observations only) subsets. A majority of the AMUSE-Field galaxies (78%) inhabits groups, enabling us to investigate the influence of group richness upon nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for isolated galaxies, and that this trend continues to cluster early-types. Keywords: black hole physics — galaxies: nuclei

1. INTRODUCTION Convincing evidence that supermassive black holes (SMBHs) are able to form in the early universe is provided by observations of high-redshift quasars (e.g., Volonteri & Rees 2006; Vestergaard & Osmer 2009; Willott et al. 2010; Treister et al. 2011). The seeds for these early SMBHs may have been produced from super- massive (e.g., Begelman 2010) or Population III stars, or from direct gas collapse (e.g., Volonteri & Natara- jan 2009), perhaps in massive protogalaxy mergers (e.g., Mayer et al. 2010; Volonteri 2010). While high-redshift quasars generally display optical/UV and X-ray proper- ties similar to those of their local analogues (e.g., Shem- mer et al. 2006), Spitzer observations indicate many are young sources (some lack hot dust) that are growing rapidly (Jiang et al. 2010). In contrast, similarly mas- sive SMBHs at more moderate redshifts are growing more slowly (e.g., Netzer et al. 2007). Indeed, the growth of SMBHs appears to be “anti-hierarchical” in the sense that active accretion is concentrated in higher/lower- mass SMBHs at earlier/later cosmological times (e.g., Heckman et al. 2004; Merloni & Heinz 2007; Shankar et al. 2009; Gallo et al. 2010; Goulding et al. 2010; Kelly et al. 2010; Lamastra et al. 2010; Schulze & Wisotzki 1 Department of Astronomy, University of Michigan, Ann Ar- bor, MI 48109, USA 2 Physics Department, University of California, Santa Bar- bara, CA 93106, USA 3 Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul, Republic of Korea 2010; Schawinski et al. 2010). The peak of the quasar space density around z ∼2 (e.g., Brown et al. 2006; Hopkins et al. 2007; Kelly et al. 2010)4 and the ∼108 yr quasar lifetime (e.g., Yu & Tremaine 2002) suggest (e.g., Soltan 1982) that “inac- tive” galactic nuclei typically also host SMBHs accret- ing at low levels and/or radiating inefficiently in a post- quasar stage which may result after much of the avail- able fuel has been consumed or expelled (e.g., Hopkins et al. 2005). The distinctions between active galactic nu- clei (AGNs), low-luminosity AGNs (Ho 1999, 2008), and formally inactive galaxies are somewhat arbitrary, but as a general guideline (which we will adhere to in this work) AGNs display bolometric, Eddington-scaled lumi- nosities in excess of a few percent, low-luminosity AGNs are in the range 10−4 < L/LEdd < 10−2, and inactive nuclei are highly sub-Eddington, with L/LEdd <∼10−4. The Milky Way is one example of a formally inactive galaxy. It is known to host a quiescent central SMBH with mass of 3.6 × 106M⊙(e.g., Sch¨odel et al. 2009) from whi

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