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Register a new userThe Growth of Black Holes: Insights From Obscured Active Galaxies
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Jenny E. Greene
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Obscured or narrow-line active galaxies offer an unobstructed view of the quasar environment in the presence of a luminous and vigorously accreting black hole. We exploit the large new sample of optically selected luminous narrow-line active galaxies from the Sloan Digital Sky Survey at redshifts 0.1 < z < 0.45, in conjunction with follow-up observations with the Low Dispersion Survey Spectrograph (LDSS3) at Magellan, to study the distributions of black hole mass and host galaxy properties in these extreme objects. We find a narrow range in black hole mass (<log M_BH/M_sun> = 8.0 +/- 0.7) and Eddington ratio (<log L/L_Edd> = -0.7 +/- 0.7) for the sample as a whole, surprisingly similar to comparable broad-line systems. In contrast, we infer a wide range in star formation properties and host morphologies for the sample, from disk-dominated to elliptical galaxies. Nearly one-quarter have highly disturbed morphologies indicative of ongoing mergers. Unlike the black holes, which are apparently experiencing significant growth, the galaxies appear to have formed the bulk of their stars at a previous epoch. On the other hand, it is clear from the lack of correlation between gaseous and stellar velocity dispersions in these systems that the host galaxy interstellar medium is far from being in virial equilibrium with the stars. While our findings cast strong doubt on the reliability of substituting gas for stellar dispersions in high luminosity active galaxies, they do provide direct evidence that luminous accreting black holes influence their surroundings on a galaxy-wide scale.
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We summarize what large surveys of the contemporary universe have taught us about the physics and phenomenology of the processes that link the formation and evolution of galaxies and their central supermassive black holes. We present a picture in which the population of AGN can be divided into two distinct populations. The Radiative-Mode AGN are associated with black holes that produce radiant energy powered by accretion at rates in excess of ~1% of the Eddington Limit. They are primarily associated with less massive black holes growing in high-density pseudo-bulges at a rate sufficient to produce the total mass budget in these black holes in ~10 Gyr. The circum-nuclear environment contains high density cold gas and associated star-formation. Major mergers are not the primary mechanism for transporting this gas inward; secular processes appear dominant. Stellar feedback will be generic in these objects and strong AGN feedback is seen only in the most powerful AGN. In Jet-Mode AGN the bulk of energetic output takes the form of collimated outflows (jets). These AGN are associated with the more massive black holes in more massive (classical) bulges and elliptical galaxies. Neither the accretion onto these black holes nor star-formation in their host bulge is significant today. These AGN are probably fueled by the accretion of slowly cooling hot gas that is limited by the feedback/heating provided by AGN radio sources. Surveys of the high-redshift universe are painting a similar picture. (Abridged).
The population of massive black holes (MBHs) in dwarf galaxies is elusive, but fundamentally important to understand the coevolution of black holes with their hosts and the formation of the first collapsed objects in the Universe. While some progress was made in determining the X-ray detected fraction of MBHs in dwarfs, with typical values ranging from $0%$ to $6%$, their overall active fraction, ${cal A}$, is still largely unconstrained. Here, we develop a theoretical model to predict the multiwavelength active fraction of MBHs in dwarf galaxies starting from first principles and based on the physical properties of the host, namely, its stellar mass and angular momentum content. We find multiwavelength active fractions for MBHs, accreting at typically low rates, ranging from $5%$ to $22%$, and increasing with the stellar mass of the host as ${cal A} sim(log_{10}M_{star})^{4.5}$. If dwarfs are characterized by low-metallicity environments, the active fraction may reach $sim 30%$ for the most massive hosts. For galaxies with stellar mass in the range $10^7<M_{star} [M_{odot}]<10^{10}$, our predictions are in agreement with occupation fractions derived from simulations and semi-analytical models. Additionally, we provide a fitting formula to predict the probability of finding an active MBH in a dwarf galaxy from observationally derived data. This model will be instrumental to guide future observational efforts to find MBHs in dwarfs. The James Webb Space Telescope, in particular, will play a crucial role in detecting MBHs in dwarfs, possibly uncovering active fractions $sim 3$ times larger than current X-ray surveys.
Massive black holes (BHs) are at once exotic and yet ubiquitous, residing in the centers of massive galaxies in the local Universe. Recent years have seen remarkable advances in our understanding of how these BHs form and grow over cosmic time, during which they are revealed as active galactic nuclei (AGN). However, despite decades of research, we still lack a coherent picture of the physical drivers of BH growth, the connection between the growth of BHs and their host galaxies, the role of large-scale environment on the fueling of BHs, and the impact of BH-driven outflows on the growth of galaxies. In this paper we review our progress in addressing these key issues, motivated by the science presented at the What Drives the Growth of Black Holes? workshop held at Durham on 26th-29th July 2010, and discuss how these questions may be tackled with current and future facilities.
Nearby galaxy surveys have long classified X-ray binaries (XRBs) by the mass category of their donor stars (high-mass and low-mass). The NuSTAR observatory, which provides imaging data at E $>10$ keV, has enabled the classification of extragalactic XRBs by their compact object type: neutron star (NS) or black hole (BH). We analyzed NuSTAR/Chandra/XMM-Newton observations from a NuSTAR-selected sample of 12 galaxies within 5 Mpc having stellar masses ($M_{star}$) $10^{7-11}$ $M_{odot}$ and star formation rates (SFR) $approx0.01-15$ $M_{odot}$ yr$^{-1}$. We detect 128 NuSTAR sources to a sensitivity of $approx10^{38}$ erg s$^{-1}$. Using NuSTAR color-intensity and color-color diagrams we classify 43 of these sources as candidate NS and 47 as candidate BH. We further subdivide BH by accretion states (soft, intermediate, and hard) and NS by weak (Z/Atoll) and strong (accreting pulsar) magnetic field. Using 8 normal (Milky Way-type) galaxies in the sample, we confirm the relation between SFR and galaxy X-ray point source luminosity in the 4-25 and 12-25 keV energy bands. We also constrain galaxy X-ray point source luminosity using the relation $L_{rm{X}}=alpha M_{star}+betatext{SFR}$, finding agreement with previous work. The XLF of all sources in the 4-25 and 12-25 keV energy bands matches with the $alpha=1.6$ slope for high-mass XRBs. We find that NS XLFs suggest a decline beginning at the Eddington limit for a 1.4 $M_{odot}$ NS, whereas the BH fraction shows an approximate monotonic increase in the 4-25 and 12-25keV energy bands. We calculate the overall ratio of BH to NS to be $approx1$ for 4-25 keV and $approx2$ for 12-25 keV.
It is well established that a dominant phase in the growth of massive galaxies occurred at high redshift and was heavily obscured by gas and dust. Many studies have explored the stellar growth of massive galaxies but few have combined these constraints with the growth of the supermassive black hole (SMBH; i.e., identified as AGN activity). In this brief contribution we highlight our work aimed at identifying AGNs in z~2 luminous dust-obscured galaxies. Using both sensitive X-ray and infrared (IR)-submillimeter (submm) observations, we show that AGN activity is common in z~2 dust-obscured systems. With a variety of techniques we have found that the majority of the AGN activity is heavily obscured, and construct diagnostics based on X-ray-IR data to identify some of the most heavily obscured AGNs in the Universe (i.e., AGNs obscured by Compton-thick material; N_H>1.5x10^24 cm^-2). On the basis of these techniques we show that SMBH growth was typically heavily obscured (N_H>10^23 cm^-2) at z~2, and find that the growth of the SMBH and spheroid was closely connected, even in the most rapidly evolving systems.
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