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Register a new userThe connection between star formation and supermassive Black Hole activity in the local Universe
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We present a study of the active galactic nucleus (AGN) activity in the local Universe (z < 0.33) and its correlation with the host galaxy properties, derived from a Sloan Digital Sky Survey (SDSS DR8) sample with spectroscopic star-formation rate (SFR) and stellar mass ($mathcal{M}_{ast}$) determination. To quantify the level of AGN activity we used X-ray information from the XMM-Newton Serendipitous Source Catalogue (3XMM DR8). Applying multiwavelength AGN selection criteria (optical BPT-diagrams, X-ray/optical ratio etc) we found that 24% of the detected sources are efficiently-accreting AGN with moderate-to-high X-ray luminosity, which are twice as likely to be hosted by star-forming galaxies than by quiescent ones. The distribution of the specific Black Hole accretion rate (sBHAR, $lambda_{mathrm{sBHAR}}$) shows that nuclear activity in local, non-AGN dominated galaxies peaks at very low accretion rates ($-4 lesssim loglambda_{mathrm{sBHAR}} lesssim -3$) in all stellar mass ranges. However, we observe systematically larger values of sBHAR for galaxies with active star-formation than for quiescent ones, as well as an increase of the mean $lambda_{mathrm{sBHAR}}$ with SFR for both star-forming and quiescent galaxies. These findings confirm the decreased level of AGN activity with cosmic time and are consistent with a scenario where both star-formation and AGN activity are fuelled by a common gas reservoir.
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We present a study of the star formation and central black hole accretion activity of the galaxies hosted in the two nearby (z$sim$0.2) rich galaxy clusters Abell 983 and 1731. Aims: We are able to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods: We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy @ 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations ($sim$ 3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results: The star forming members of the two clusters present star formation rates comparable with those measured in coeval field galaxies. The analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with respect to the more uniform distribution of A983. The emerging picture is compatible with A983 being a fully evolved cluster, in contrast with the still actively accreting A1731. Conclusions: The analysis of the specific star formation rate reveals evidence of on-going galaxy pre-processing along A1731s filament-like structure. Furthermore, the decrease in the number of star forming galaxies and AGN towards the cluster cores suggests that the cluster environment is accelerating the ageing process of galaxies and blocking further accretion of the cold gas that fuels both star formation and black hole accretion activity.
We use a sample built on the SDSS DR7 catalogue and the bulge-disc decomposition of Simard et al. (2011) to study how the bulge and disc components contribute to the parent galaxys star formation activity, by determining its position in the star formation rate (SFR) - stellar mass (M$_{star}$) plane at 0.02$<z<$0.1. We use the bulge and disc colours as proxy for their SFRs. We study the mean galaxy bulge-total mass ratio (B/T) as a function of the residual from the MS ($Delta_{MS}$) and find that the B/T-$Delta_{MS}$ relation exhibits a parabola-like shape with the peak of the MS corresponding to the lowest B/Ts at any stellar mass. The lower and upper envelop of the MS are populated by galaxies with similar B/T, velocity dispersion and concentration ($R_{90}/R_{50}$) values. Bulges above the MS are characterised by blue colours or, when red, by a high level of dust obscuration, thus indicating that in both cases they are actively star forming. When on the MS or below it, bulges are mostly red and dead. At stellar masses above $10^{10.5} $M$_{odot}$, bulges on the MS or in the green valley tend to be significantly redder than their counterparts in the quiescence region, despite similar levels of dust obscuration. The disc color anti-correlates at any mass with the distance from the MS, getting redder when approaching the MS lower envelope and the quiescence region. We conclude that the position of a galaxy in the LogSFR-LogM$_{star}$ plane depends on the star formation activity of its components: above the MS both bulge and disk are actively star forming. The nuclear activity is the first to be suppressed, moving the galaxies on the MS. Once the disk stops forming stars as well, the galaxy moves below the MS and eventually to the quiescence region. This is confirmed by a large fraction ($sim45%$) of passive galaxies with a secure two component morphology.
We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2-1) and [N II] 205 um lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ~6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2-1) line, down to a level twelve times lower than the expected value for star forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated through much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, though we argue unlikely, that the ensemble of fine structure lines are emitted from the region heated by the AGN.
Numerical models of gas inflow towards a supermassive black hole (SMBH) show that star formation may occur in such an environment through the growth of a gravitationally unstable gas disc. We consider the effect of nuclear activity on such a scenario. We present the first three-dimensional grid-based radiative hydrodynamic simulations of direct collisions between infalling gas streams and a $4 times 10^6~text{M}_odot$ SMBH, using ray-tracing to incorporate radiation consistent with an active galactic nucleus (AGN). We assume inflow masses of $ approx 10^5~text{M}_odot$ and explore radiation fields of 10% and 100% of the Eddington luminosity ($L_text{edd}$). We follow our models to the point of central gas disc formation preceding star formation and use the Toomre Q parameter ($Q_T$) to test for gravitational instability. We find that radiation pressure from UV photons inhibits inflow. Yet, for weak radiation fields, a central disc forms on timescales similar to that of models without feedback. Average densities of $> 10^{8}~text{cm}^{-3}$ limit photo-heating to the disc surface allowing for $Q_Tapprox1$. For strong radiation fields, the disc forms more gradually resulting in lower surface densities and larger $Q_T$ values. Mass accretion rates in our models are consistent with 1%--60% of the Eddington limit, thus we conclude that it is unlikely that radiative feedback from AGN activity would inhibit circumnuclear star formation arising from a massive inflow event.
Galaxies grow their supermassive black holes in concert with their stars, although the relationship between these major galactic components is poorly understood. Observations of the cosmic growth of stars and black holes in galaxies suffer from disjoint samples and the strong effects of dust attenuation. The thermal infrared holds incredible potential for simultaneously measuring both the star formation and black hole accretion rates in large samples of galaxies covering a wide range of physical conditions. Spitzer demonstrated this potential at low redshift, and by observing some of the most luminous galaxies at z~2. JWST will apply these methods to normal galaxies at these epochs, but will not be able to generate large spectroscopic samples or access the thermal infrared at high-redshift. An order of magnitude gap in our wavelength coverage will persist between JWST and ALMA. A large, cold infrared telescope can fill this gap to determine when (in cosmic time), and where (within the cosmic web), stars and black holes co-evolve, by measuring these processes simultaneously in statistically complete and unbiased samples of galaxies to z>8. A next-generation radio interferometer will have the resolution and sensitivity to measure star-formation and nuclear accretion in even the dustiest galaxies. Together, the thermal infrared and radio can uniquely determine how stars and supermassive blackholes co-evolve in galaxies over cosmic time.
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