A Constant Ratio between Black Hole Accretion and Star Formation in IR-bright AGNs (original) (raw)
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The Relationship between black hole accretion and host star formation in dusty AGNs
arXiv (Cornell University), 2015
We report the relationship between the luminosities of active galactic nuclei (AGNs) and the rates of star formation (SF) for a sample of 323 far-infrared (FIR)-detected AGNs. This sample has a redshift range of 0.2 < z < 2.5, and spans three orders of magnitude in luminosity, L X ∼ 10 42−45 erg s −1. We find that in AGN hosts, the total IR luminosity (8-1000 µm) has a significant AGN contribution (average∼20%), and we suggest using the FIR luminosity (30-1000 µm) as a more reliable star formation rate (SFR) estimator. We also conclude that monochromatic luminosities at 60 and 100 µ m are also good SFR indicators with negligible AGN contributions, and are less sensitive than integrated infrared luminosities to the shape of the AGN SED, which is uncertain at λ >100 µm. Significant bivariate L X-L IR correlations are found, which remain significant in the combined sample when using residual partial correlation analysis to account for the inherent redshift dependence. No redshift or mass dependence is found for the ratio between SFR and black hole accretion rate (BHAR), which has a mean and scatter of log (SFR/BHAR) = 3.1 ± 0.5, agreeing with the local mass ratio between supermassive black hole and host galaxies. The large scatter in this ratio and the strong AGN-SF correlation found in these IR-bright AGNs are consistent with the scenario of an AGN-SF dependence on a common gas supply, regardless of the evolutionary model.
Monthly Notices of the Royal Astronomical Society, 2010
We investigate the far-infrared (FIR) properties of X-ray sources detected in the Chandra Deep Field-South (CDF-S) survey using the ultradeep 70 and 24 μm Spitzer observations taken in this field. Since only 30 (i.e. ≈10 per cent) of the 266 X-ray sources in the region of the 70 μm observations are detected at 70 μm, we rely on stacking analyses of the 70 μm data to characterize the average 70 μm properties of the X-ray sources as a function of redshift, X-ray luminosity and X-ray absorption. Using Spitzer-IRS data of the Swift-Burst Alert Telescope (BAT) sample of z ≈ 0 active galactic nuclei (AGNs), we show that the 70/24 μm flux ratio can distinguish between AGN-dominated and starburst-dominated systems out to z ≈ 1.5. Among the X-ray sources detected at 70 μm, we note a large scatter in the observed 70/24 μm flux ratios, spanning almost a factor of 10 at similar redshifts, irrespective of object classification, suggesting a range of AGN:starburst ratios. From stacking analyses we find that the average observed 70/24 μm flux ratios of AGNs out to an average redshift of 1.5 are similar to z ≈ 0 AGNs with similar X-ray luminosities (L X = 10 42−44 erg s −1) and absorbing column densities (N H ≤ 10 23 cm −2). Furthermore, both high-redshift and z ≈ 0 AGNs follow the same tendency towards warmer 70/24 μm colours with increasing X-ray luminosity (L X). From analyses of the Swift-BAT sample of z ≈ 0 AGNs, we note that the 70 μm flux can be used to determine the IR (8-1000 μm) luminosities of high-redshift AGNs. We use this information to show that L X = 10 42−43 erg s −1 AGNs at high redshifts (z = 1-2) have IR to X-ray luminosity ratios (L IR /L X) that are, on average, 4.7 +10.2 −2.0 and 12.7 +7.1 −2.6 times higher than AGNs with similar X-ray luminosities at z = 0.5-1 and ≈0, respectively. By comparison, we find that the L IR /L X ratios of L X = 10 43−44 erg s −1 AGNs remain largely unchanged across this same redshift interval. We explore the consequences that these results may have on the identification of distant, potentially Compton-thick AGNs using L IR /L X ratios. In addition, we discuss possible scenarios for the observed increase in the L IR /L X ratio with redshift, including changes in the dust covering factor of AGNs and/or the star formation rates of their host galaxies. Finally, we show how deep observations to be undertaken by the Herschel Space Observatory will enable us to discriminate between these proposed scenarios and also identify Compton-thick AGNs at high redshifts.
Monthly Notices of the Royal Astronomical Society, 2017
Nuclear starbursts and active galactic nucleus (AGN) activity are the main heating processes in luminous infrared galaxies (LIRGs) and their relationship is fundamental to understand galaxy evolution. In this paper, we study the star formation and AGN activity of a sample of 11 local LIRGs imaged with subarcsecond angular resolution at radio (8.4 GHz) and near-infrared (2.2 µm) wavelengths. This allows us to characterize the central kpc of these galaxies with a spatial resolution of 100 pc. In general, we find a good spatial correlation between the radio and the near-IR emission, although radio emission tends to be more concentrated in the nuclear regions. Additionally, we use an Markov Chain Monte Carlo code to model their multiwavelength spectral energy distribution (SED) using template libraries of starburst, AGN and spheroidal/cirrus models, determining the luminosity contribution of each component, and finding that all sources in our sample are starburst-dominated, except for NGC 6926 with an AGN contribution of 64 per cent. Our sources show high star formation rates (40-167 M yr −1), supernova rates (0.4-2.0 SN yr −1) and similar starburst ages (13-29 Myr), except for the young starburst (9 Myr) in NGC 6926. A comparison of our derived starforming parameters with estimates obtained from different IR and radio tracers shows an overall consistency among the different star formation tracers. AGN tracers based on mid-IR, high-ionization line ratios also show an overall agreement with our SED model fit estimates for the AGN. Finally, we use our wide-band Very Large Array observations to determine pixel-by-pixel radio spectral indices for all galaxies in our sample, finding a typical median value (α −0.8) for synchrotron-powered LIRGs.
2009
From stacking analysis we find that both high redshift and z~0 AGNs follow the same tendency toward warmer 70um/24um colours with increasing X-ray luminosity (L_X). We also show that the 70um flux can be used to determine the infrared (8-1000um) luminosities of high redshift AGNs. We use this information to show that L_X=10^{42-43} erg/s AGNs at high redshifts (z=1-2) have infrared to X-ray luminosity ratios (hereafter, L_IR/L_X) that are, on average, 4.7_{-2.0}^{+10.2} and 12.7^{+7.1}_{-2.6} times higher than AGNs with similar X-ray luminosities at z=0.5-1 and z~0, respectively. By comparison, we find that the L_IR/L_X ratios of L_X=10^{43-44} erg/s AGNs remain largely unchanged across this same redshift interval. We explore the consequences that these results may have on the identification of distant, potentially Compton thick AGNs using L_IR/L_X ratios. We discuss possible scenarios for the observed increase in the L_IR/L_X ratio with redshift, including changes in the dust covering factor of AGNs and/or the star formation rates of their host galaxies. Finally, we show how deep observations to be undertaken by the Herschel Space Observatory will enable us to discriminate between these proposed scenarios and also identify Compton-thick AGNs at high redshifts.
Monthly Notices of the Royal Astronomical Society, 2012
We use Herschel-PACS far-infrared data, combined with previous multi-band information and mid-IR spectra, to properly account for the presence of an active nucleus and constrain its energetic contribution in luminous infrared (IR) sources at z ∼ 2. The sample is composed of 24 sources in the GOODS-South field, with typical IR luminosity of 10 12 L ⊙ . Data from the 4 Ms Chandra X-ray imaging in this field are also used to identify and characterize AGN emission. We reproduce the observed spectral energy distribution (SED), decomposed into a host-galaxy and an AGN component. A smooth-torus model for circum-nuclear dust is used to account for the direct and re-processed contribution from the AGN. We confirm that galaxies with typical L 8−1000µm ∼10 12 L ⊙ at z∼2 are powered predominantly by star-formation. An AGN component is present in nine objects (∼35% of the sample) at the 3σ confidence level, but its contribution to the 8-1000 µm emission accounts for only ∼5% of the energy budget. The AGN contribution rises to ∼23% over the 5-30 µm range (in agreement with Spitzer IRS results) and to ∼60% over the narrow 2-6 µm range. The presence of an AGN is confirmed by X-ray data for 3 (out of nine) sources, with X-ray spectral analysis indicating the presence of significant absorption, i.e. N H ∼10 23 − 10 24 cm −2 . An additional source shows indications of obscured AGN emission from X-ray data. The comparison between the mid-IR-derived X-ray luminosities and those obtained from X-ray data suggests that obscuration is likely present also in the remaining six sources that harbour an AGN according to the SEDfitting analysis.
2021
Context. Active Galactic Nuclei (AGN) are thought to be responsible for the suppression of star formation in massive ∼ 10^10 Msun galaxies. While this process is a key feature in numerical simulations of galaxy formation, it is not yet unambiguously confirmed in observational studies. Aims. Characterization of the star formation rate (SFR) in AGN host galaxies is challenging as AGN light contaminates most SFR tracers. Furthermore, the various SFR tracers are sensitive to different timescales of star formation from ∼a few to 100 Myr. We aim to obtain and compare SFR estimates from different tracers for AGN host galaxies in the Close AGN Reference Survey (CARS) to provide new observational insights into the recent SFR history of those systems. Methods. We construct integrated panchromatic spectral energy distributions (SED) to measure the FIR luminosity as a tracer for the recent (<100 Myr) SFR. In addition we use integral-field unit (IFU) observation of the CARS targets to employ the Hα luminosity decontaminated by AGN excitation as a proxy for the current (<5Myr) SFR. Results. We find that significant differences in specific SFR of the AGN host galaxies as compared with the larger galaxy population disappear once cold gas mass, in addition to stellar mass, is used to predict the SFR for a specific AGN host. Only a tentative trend with the inclination of the host galaxy is remaining such that SFR appears slightly lower than expected when the galaxies of unobscured AGN appear more edge-on along our line-of-sight, particular for dust-insensitive FIR-based SFRs. We identify individual galaxies with significant difference in their SFR which can be related to a recent enhancement or decline in their SFR history that might be related to various processes including interactions, gas consumption, outflows and AGN feedback. Conclusions. AGN can occur in various stages of galaxy evolution which makes it difficult to relate the SFR solely to the impact of the AGN. Our study shows that stellar mass alone is an insufficient parameter to estimate the expected SFR of an AGN host galaxy compared to the underlying non-AGN galaxy population. We do not find any strong evidence for a global positive or negative AGN feedback in the CARS sample. However, there is tentative evidence that 1) the relative orientation of the AGN engine with respect to the host galaxies might alter the efficiency of AGN feedback and 2) the recent SFH is an additional tool to identify rapid changes in galaxy growth driven by the AGN or other processes.
2012
The growth of supermassive black holes and their host galaxies are thought to be linked, but the precise nature of this symbiotic relationship is still poorly understood. Both observations and simulations of galaxy formation suggest that the energy input from active galactic nuclei (AGN), as the central supermassive black hole accretes material and grows, heats the interstellar material and suppresses star formation. In this Letter, we show that most host galaxies of moderate-luminosity supermassive black holes in the local universe have intermediate optical colors that imply the host galaxies are transitioning from star formation to quiescence, the first time this has been shown to be true for all AGN independent of obscuration. The intermediate colors suggest that star formation in the host galaxies ceased roughly 100 Myr ago. This result indicates that either the AGN are very long-lived, accreting for more than 1 Gyr beyond the end of star formation, or there is a ∼100 Myr time d...
HerMES: Far infrared properties of known AGN in the HerMES fields
Astronomy & Astrophysics, 2010
Nuclear and starburst activity are known to often occur concomitantly. Herschel-SPIRE provides sampling of the FIR SEDs of type 1 and type 2 AGN, allowing for the separation between the hot dust (torus) and cold dust (starburst) emission. We study large samples of spectroscopically confirmed type 1 and type 2 AGN lying within the Herschel Multi-tiered Extragalactic Survey (HerMES) fields observed during the science demonstration phase, aiming to understand their FIR colour distributions and constrain their starburst contributions. We find that one third of the spectroscopically confirmed AGN in the HerMES fields have 5-sigma detections at 250um, in agreement with previous (sub)mm AGN studies. Their combined Spitzer-MIPS and Herschel-SPIRE colours - specifically S(250)/S(70) vs. S(70)/S(24) - quite clearly separate them from the non-AGN, star-forming galaxy population, as their 24-um flux is dominated by the hot torus emission. However, their SPIRE colours alone do not differ from those of non-AGN galaxies. SED fitting shows that all those AGN need a starburst component to fully account for their FIR emission. For objects at z > 2, we find a correlation between the infrared luminosity attributed to the starburst component, L(SB), and the AGN accretion luminosity, L(acc), with L(SB) propto L(acc)^0.35. Type 2 AGN detected at 250um show on average higher L(SB) than type 1 objects but their number is still too low to establish whether this trend indicates stronger star-formation activity.
2009
We present the results of Spitzer IRS infrared 5-35 micron low-resolution spectroscopic energy diagnostics of ultraluminous infrared galaxies (ULIRGs) at z > 0.15, classified optically as non-Seyferts. Based on the equivalent widths of polycyclic aromatic hydrocarbon emission and the optical depths of silicate dust absorption features, we searched for signatures of intrinsically luminous, but optically elusive, buried AGNs in these optically non-Seyfert ULIRGs. We then combined the results with those of non-Seyfert ULIRGs at z < 0.15 and non-Seyfert galaxies with infrared luminosities L(IR) < 10^12Lsun. We found that the energetic importance of buried AGNs clearly increases with galaxy infrared luminosity, becoming suddenly discernible in ULIRGs with L(IR) > 10{12}Lsun. For ULIRGs with buried AGN signatures, a significant fraction of infrared luminosities can be accounted for by detected buried AGN and modestly-obscured (Av < 20 mag) starburst activity. The implied masses of spheroidal stellar components in galaxies for which buried AGNs become important roughly correspond to the value separating red massive and blue, less-massive galaxies in the local universe. Our results may support the widely-proposed AGN-feedback scenario as the origin of galaxy downsizing phenomena, where galaxies with currently larger stellar masses previously had higher AGN energetic contributions and star-formation-originating infrared luminosities, and have finished their major star-formation more quickly, due to stronger AGN feedback.
Star formation in AGN hosts in GOODS-N
Astronomy and Astrophysics, 2010
Sensitive Herschel far-infrared observations can break degeneracies that were inherent to previous studies of star formation in highz AGN hosts. Combining PACS 100 and 160µm observations of the GOODS-N field with 2Msec Chandra data, we detect ∼20% of X-ray AGN individually at > 3σ. The host far-infrared luminosity of AGN with L 2−10keV ≈ 10 43 erg s −1 increases with redshift by an order of magnitude from z=0 to z∼1. In contrast, there is little dependence of far-infrared luminosity on AGN luminosity, for L 2−10keV 10 44 erg s −1 AGN at z 1. We do not find a dependence of far-infrared luminosity on X-ray obscuring column, for our sample which is dominated by L 2−10keV < 10 44 erg s −1 AGN. In conjunction with properties of local and luminous high-z AGN, we interpret these results as reflecting the interplay between two paths of AGN/host coevolution. A correlation of AGN luminosity and host star formation is traced locally over a wide range of luminosities and also extends to luminous high z AGN. This correlation reflects an evolutionary connection, likely via merging. For lower AGN luminosities, star formation is similar to that in non-active massive galaxies and shows little dependence on AGN luminosity. The level of this secular, non-merger driven star formation increasingly dominates over the correlation at increasing redshift.