L. K. Hunt

The relation between black hole mass, bulge mass, and near-infrared luminosity

We present new accurate near-infrared (NIR) spheroid (bulge) structural parameters obtained by a two-dimensional image analysis of all galaxies with a direct black hole (BH) mass determination. As expected, NIR bulge luminosities Lbul and BH masses are tightly correlated, and if we consider only those galaxies with a secure BH mass measurement and an accurate Lbul (27 objects), the spread of MBH-Lbul is similar to MBH-σe, where σe is the effective stellar velocity dispersion. We find an intrinsic rms scatter of 0.3 dex in log MBH. By combining the bulge effective radii Re measured in our analysis with σe, we find a tight linear correlation (rms 0.25 dex) between MBH and the virial bulge mass (Reσ), with MBH/Mbul ~ 0.002. A partial correlation analysis shows that MBH depends on both σe and Re and that both variables are necessary to drive the correlations between MBH and other bulge properties.

Local supermassive black holes, relics of active galactic nuclei and the X-ray background

We quantify the importance of mass accretion during AGN phases in the growth of supermassive black holes (BH) by comparing the mass function of black holes in the local universe with that expected from AGN relics, which are black holes grown entirely with mass accretion during AGN phases. The local BH mass function (BHMF) is estimated by applying the well-known correlations between BH mass, bulge luminosity and stellar velocity dispersion to galaxy luminosity and velocity functions. We find that different correlations provide the same BHMF only if they have the same intrinsic dispersion. The density of supermassive black holes in the local universe which we estimate is ρBH = 4.6 +1.9 −1.4 h 2.7 × 10 5 M⊙ Mpc −3 . The relic BHMF is derived from the continuity equation with the only assumption that AGN activity is due to accretion onto massive BH’s and that merging is not important. We find that the relic BHMF at z = 0 is generated mainly at z 10 9 M⊙ but can become as large as ∼ 10 9 yr for the lowest acceptable ǫ and λ values.

THE ARECIBO LEGACY FAST ALFA SURVEY. I. SCIENCE GOALS, SURVEY DESIGN, AND STRATEGY

The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims to map ~7000 deg2 of the high Galactic latitude sky visible from Arecibo, providing a H I line spectral database covering the redshift range between -1600 and 18,000 km s-1 with ~5 km s-1 resolution. Exploiting Arecibos large collecting area and small beam size, ALFALFA is specifically designed to probe the faint end of the H I mass function in the local universe and will provide a census of H I in the surveyed sky area to faint flux limits, making it especially useful in synergy with wide-area surveys conducted at other wavelengths. ALFALFA will also provide the basis for studies of the dynamics of galaxies within the Local Supercluster and nearby superclusters, allow measurement of the H I diameter function, and enable a first wide-area blind search for local H I tidal features, H I absorbers at z < 0.06, and OH megamasers in the redshift range 0.16 < z < 0.25. Although completion of the survey will require some 5 years, public access to the ALFALFA data and data products will be provided in a timely manner, thus allowing its application for studies beyond those targeted by the ALFALFA collaboration. ALFALFA adopts a two-pass, minimum intrusion, drift scan observing technique that samples the same region of sky at two separate epochs to aid in the discrimination of cosmic signals from noise and terrestrial interference. Survey simulations, which take into account large-scale structure in the mass distribution and incorporate experience with the ALFA system gained from tests conducted during its commissioning phase, suggest that ALFALFA will detect on the order of 20,000 extragalactic H I line sources out to z ~ 0.06, including several hundred with H I masses M < 107.5 M⊙.

GRB 090423 at a redshift of z ≈ 8.1

Gamma-ray bursts (GRBs) are produced by rare types of massive stellar explosion. Their rapidly fading afterglows are often bright enough at optical wavelengths that they are detectable at cosmological distances. Hitherto, the highest known redshift for a GRB was z = 6.7 (ref. 1), for GRB 080913, and for a galaxy was z = 6.96 (ref. 2). Here we report observations of GRB 090423 and the near-infrared spectroscopic measurement of its redshift, z = . This burst happened when the Universe was only about 4 per cent of its current age. Its properties are similar to those of GRBs observed at low/intermediate redshifts, suggesting that the mechanisms and progenitors that gave rise to this burst about 600,000,000 years after the Big Bang are not markedly different from those producing GRBs about 10,000,000,000 years later.

The Spitzer/IRAC view of black hole–bulge scaling relations

We present a mid-infrared investigation of the scaling relations between supermassive black hole masses (M BH ) and the structural parameters of the host spheroids in local galaxies. This work is based on 2D bulge-disc decompositions of Spitzer/IRAC 3.6 μm images of 57 galaxies with M BH estimates. We first verify the accuracy of our decomposition by examining the Fundamental Plane (FP) of spheroids at 3.6 μm. Our estimates of effective radii (R e ) and average surface brightnesses, combined with velocity dispersions from the literature, define a FP relation consistent with previous determinations but doubling the observed range in R e . None of our galaxies is an outlier of the FP, demonstrating the accuracy of our bulge-disc decomposition which also allows us to independently identify pseudo-bulges in our sample. We calibrate M/L at 3.6 μm by using the tight M dyn ―L bul relation (∼0.1 dex intrinsic dispersion) and find that no colour corrections are required to estimate the stellar mass. The 3.6 μm luminosity is thus the best tracer of stellar mass yet studied. We then explore the connection between M BH and bulge structural parameters (luminosity, mass, effective radius). We find tight correlations of M BH with both 3.6 μm bulge luminosity and dynamical mass (M BH /M dyn ∼ 1/1000), with intrinsic dispersions of ∼0.35 dex, similar to the M BH ―σ relation. Our results are consistent with previous determinations at shorter wavelengths. By using our calibrated M/L, we rescale M BH ―L bul to obtain the M BH ―M * relation, which can be used as the local reference for high-z studies which probe the cosmic evolution of M BH ―galaxy relations and where the stellar mass is inferred directly from luminosity measurements. The analysis of pseudo-bulges shows that four out of nine lie on the scaling relations within the observed scatter, while those with small M BH are significantly displaced. We explore the different origins for such behaviour while considering the possibility of nuclear morphological components not reproduced by our 2D decomposition.

The dust scaling relations of the Herschel Reference Survey

We combine new Herschel/SPIRE sub-millimeter observations with existing multiwavelength data to investigate the dust scaling relations of the Herschel Reference Survey, a magnitude-, volume-limited sample of similar to 300 nearby galaxies in different environments. We show that the dust-to-stellar mass ratio anti-correlates with stellar mass, stellar mass surface density and NUV - r colour across the whole range of parameters covered by our sample. Moreover, the dust-to-stellar mass ratio decreases significantly when moving from late-to early-type galaxies. These scaling relations are similar to those observed for the Hi gas-fraction, supporting the idea that the cold dust is tightly coupled to the cold atomic gas component in the interstellar medium. We also find a weak increase of the dust-to-Hi mass ratio with stellar mass and colour but no trend is seen with stellar mass surface density. By comparing galaxies in different environments we show that, although these scaling relations are followed by both cluster and field galaxies, Hi-deficient systems have, at fixed stellar mass, stellar mass surface density and morphological type systematically lower dust-to-stellar mass and higher dust-to-Hi mass ratios than Hi-normal/field galaxies. This provides clear evidence that dust is removed from the star-forming disk of cluster galaxies but the effect of the environment is less strong than what is observed in the case of the Hi disk. Such effects naturally arise if the dust disk is less extended than the Hi and follows more closely the distribution of the molecular gas phase, i.e., if the dust-to-atomic gas ratio monotonically decreases with distance from the galactic center.

THE EMISSION BY DUST AND STARS OF NEARBY GALAXIES IN THE HERSCHEL KINGFISH SURVEY

Using new far-infrared imaging from the Herschel Space Observatory with ancillary data from ultraviolet (UV) to submillimeter wavelengths, we estimate the total emission from dust and stars of 62 nearby galaxies in the KINGFISH survey in a way that is as empirical and model independent as possible. We collect and exploit these data in order to measure from the spectral energy distributions (SEDs) precisely how much stellar radiation is intercepted and re-radiated by dust, and how this quantity varies with galaxy properties. By including SPIRE data, we are more sensitive to emission from cold dust grains than previous analyses at shorter wavelengths, allowing for more accurate estimates of dust temperatures and masses. The dust/stellar flux ratio, which we measure by integrating the SEDs, has a range of nearly three decades (from 10^(−2.2) to 10^(0.5)). The inclusion of SPIRE data shows that estimates based on data not reaching these far-IR wavelengths are biased low by 17% on average. We find that the dust/stellar flux ratio varies with morphology and total infrared (IR) luminosity, with dwarf galaxies having faint luminosities, spirals having relatively high dust/stellar ratios and IR luminosities, and some early types having low dust/stellar ratios. We also find that dust/stellar flux ratios are related to gas-phase metallicity (log(f_(dust)/f_∗) = −0.66 ± 0.08 and −0.22 ± 0.12 for metal-poor and intermediate-metallicity galaxies, respectively), while the dust/stellar mass ratios are less so (differing by ≈0.2 dex); the more metal-rich galaxies span a much wider range of the flux ratios. In addition, the substantial scatter between dust/stellar flux and dust/stellar mass indicates that the former is a poor proxy of the latter. Comparing the dust/stellar flux ratios and dust temperatures, we also show that early types tend to have slightly warmer temperatures (by up to 5 K) than spiral galaxies, which may be due to more intense interstellar radiation fields, or possibly to different dust grain compositions. Finally, we show that early types and early-type spirals have a strong correlation between the dust/stellar flux ratio and specific star formation rate, which suggests that the relatively bright far-IR emission of some of these galaxies is due to ongoing (if limited) star formation as well as to the radiation field from older stars, which is heating the dust grains.

The Herschel Virgo Cluster Survey - II. Truncated dust disks in H I-deficient spirals

By combining Herschel-SPIRE observations obtained as part of the Herschel Virgo Cluster Survey with 21 cm Hi data from the literature, we investigate the role of the cluster environment on the dust content of Virgo spiral galaxies. We show for the first time that the extent of the dust disk is significantly reduced in Hi-deficient galaxies, following remarkably well the observed “truncation” of the Hi disk. The ratio of the submillimetre-to-optical diameter correlates with the Hi-deficiency, suggesting that the cluster environment is able to strip dust as well as gas. These results provide important insights not only into the evolution of cluster galaxies but also into the metal enrichment of the intra-cluster medium.

ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433

We report ALMA observations of CO(3-2) emission in the Seyfert 2 galaxy NGC 1433 at the unprecedented spatial resolution of 0: 5 = 24 pc. Our aim is to probe AGN (active galactic nucleus) feeding and feedback phenomena through the morphology and dynamics of the gas inside the central kpc. The galaxy NGC 1433 is a strongly barred spiral with three resonant rings: one at the ultra-harmonic resonance near corotation, and the others at the outer and inner Lindblad resonances (OLR and ILR). A nuclear bar of 400 pc radius is embedded in the large-scale primary bar. The CO map, which covers the whole nuclear region (nuclear bar and ring), reveals a nuclear gaseous spiral structure, inside the nuclear ring encircling the nuclear stellar bar. This gaseous spiral is well correlated with the dusty spiral seen in Hubble Space Telescope images. The nuclear spiral winds up in a pseudo-ring at 200 pc radius, which might correspond to the inner ILR. Continuum emission is detected at 0.87 mm only at the very centre, and its origin is more likely thermal dust emission than non-thermal emission from the AGN. It might correspond to the molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4-3) and HCO + (4-3) lines were observed simultaneously, but only upper limits are derived, with a ratio to the CO(3-2) line lower than 1/60 at 3 , indicating a relatively low abundance of very dense gas. The kinematics of the gas over the nuclear disk reveal rather regular rotation only slightly perturbed by streaming motions due to the spiral; the primary and secondary bars are too closely aligned with the galaxy major or minor axis to leave a signature in the projected velocities. Near the nucleus, there is an intense high-velocity CO emission feature redshifted to 200 km/s (if located in the plane), with a blue-shifted counterpart, at 2 00 (100 pc) from the centre. While the CO spectra are quite narrow in the centre, this wide component is interpreted as an outflow involving a molecular mass of 3.6 10 6 M and a flow rate 7 M /yr. The flow could be in part driven by the central star formation, but is mainly boosted by the AGN through its radio jets.

The Herschel Virgo Cluster Survey – VIII. The Bright Galaxy Sample★

We describe the Herschel Virgo Cluster Survey and the first data that cover the complete survey area (four 4 x 4 deg2 regions). We use these data to measure and compare the global far-infrared properties of 78 optically bright galaxies that are selected at 500 mu m and detected in all five far-infrared bands. We show that our measurements and calibration are broadly consistent with previous data obtained by the IRAS, ISO, Spitzer and Planck. We use SPIRE and PACS photometry data to produce 100-, 160-, 250-, 350- and 500-mu m cluster luminosity distributions. These luminosity distributions are not power laws, but peaked, with small numbers of both faint and bright galaxies. We measure a cluster 100500 mu m far-infrared luminosity density of 1.6(7.0) +/- 0.2 x 10(9) L Mpc(-3). This compares to a cluster 0.42.5 mu m optical luminosity density of 5.0(20.0) x 10(9) L Mpc(-3), some 3.2(2.9) times larger than the far-infrared. A typical photon originates from an optical depth of 0.4 +/- 0.1. Most of our sample galaxies are well fitted by a single modified blackbody (beta= 2), leading to a mean dust mass of log M-Dust= 7.31 M and temperature of 20.0 K. We also derive both stellar and atomic hydrogen masses from which we calculate mean values for the star-to-gas (atomic) and gas (atomic)-to-dust mass ratios of 15.1 and 58.2, respectively. Using our derived dust, atomic gas and stellar masses, we estimate cluster mass densities of 8.6(27.8) x 106, 4.6(13.9) x 108 and 7.8(29.7) x 109 M Mpc-3 for dust, atomic gas and stars, respectively. These values are higher than those derived for field galaxies by factors of 39(126), 6(18) and 34(129), respectively. In the above, the luminosity/mass densities are given using the whole sample with the values in brackets using just those galaxies that lie between 17 and 23 Mpc. We provide a data table of flux densities in all the Herschel bands for all 78 bright Virgo Cluster galaxies.