Christian Henkel

PRECISE BLACK HOLE MASSES FROM MEGAMASER DISKS: BLACK HOLE-BULGE RELATIONS AT LOW MASS

The black hole (BH)-bulge correlations have greatly influenced the last decade of efforts to understand galaxy evolution. Current knowledge of these correlations is limited predominantly to high BH masses (M BH108 M ☉) that can be measured using direct stellar, gas, and maser kinematics. These objects, however, do not represent the demographics of more typical L < L* galaxies. This study transcends prior limitations to probe BHs that are an order of magnitude lower in mass, using BH mass measurements derived from the dynamics of H2O megamasers in circumnuclear disks. The masers trace the Keplerian rotation of circumnuclear molecular disks starting at radii of a few tenths of a pc from the central BH. Modeling of the rotation curves, presented by Kuo et al., yields BH masses with exquisite precision. We present stellar velocity dispersion measurements for a sample of nine megamaser disk galaxies based on long-slit observations using the B&C spectrograph on the Dupont telescope and the Dual Imaging Spectrograph on the 3.5 m telescope at Apache Point. We also perform bulge-to-disk decomposition of a subset of five of these galaxies with Sloan Digital Sky Survey imaging. The maser galaxies as a group fall below the M BH-σ* relation defined by elliptical galaxies. We show, now with very precise BH mass measurements, that the low-scatter power-law relation between M BH and σ* seen in elliptical galaxies is not universal. The elliptical galaxy M BH-σ* relation cannot be used to derive the BH mass function at low mass or the zero point for active BH masses. The processes (perhaps BH self-regulation or minor merging) that operate at higher mass have not effectively established an M BH-σ* relation in this low-mass regime.

CO(J = 1→0) in z > 2 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs

We present ^(12)CO(J = 1 → 0) observations of the high-redshift quasi-stellar objects (QSOs) BR 1202-0725 (z = 4.69), PSS J2322+1944 (z = 4.12), and APM 08279+5255 (z = 3.91) using the NRAO Green Bank Telescope (GBT) and the MPIfR Effelsberg 100 m telescope. We detect, for the first time, the CO ground-level transition in BR 1202-0725. For PSS J2322+1944 and APM 08279+5255, our observations result in line fluxes that are consistent with previous NRAO Very Large Array (VLA) observations, but they reveal the full line profiles. We report a typical lensing-corrected velocity-integrated intrinsic ^(12)CO(J = 1 → 0) line luminosity of L_(CO) = 5 × 10^(10) K km s^(-1) pc^2 and a typical total H_2 mass of M(H_2) = 4 × 10^(10) M_☉ for the sources in our sample. The CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies, leading to a combined solution of log L_(FIR) = (1.39 ± 0.05) log L_(CO) - 1.76. It has previously been suggested that the molecular gas reservoirs in some quasar host galaxies may exhibit luminous, extended ^(12)CO(J = 1 → 0) components that are not observed in the higher J CO transitions. Using the line profiles and the total intensities of our observations and large velocity gradient (LVG) models based on previous results for higher J CO transitions, we derive that emission from all CO transitions is described well by a single gas component in which all molecular gas is concentrated in a compact nuclear region. Thus, our observations and models show no indication of a luminous extended, low surface brightness molecular gas component in any of the high-redshift QSOs in our sample. If such extended components exist, their contribution to the overall luminosity is limited to at most 30%.

The Geometric Distance and Proper Motion of the Triangulum Galaxy (M33)

We measured the angular rotation and proper motion of the Triangulum Galaxy (M33) with the Very Long Baseline Array by observing two H2O masers on opposite sides of the galaxy. By comparing the angular rotation rate with the inclination and rotation speed, we obtained a distance of 730 ± 168 kiloparsecs. This distance is consistent with the most recent Cepheid distance measurement. M33 is moving with a velocity of 190 ± 59 kilometers per second relative to the Milky Way. These measurements promise a method to determine dynamical models for the Local Group and the mass and dark-matter halos of M31, M33, and the Milky Way.

The Temperature Distribution of Dense Molecular Gas in the Center of NGC 253

We present interferometric maps of ammonia (NH3) of the nearby starburst galaxy NGC 253. The observations have been taken with the Australia Telescope Compact Array and include the para-NH3 (1, 1) and (2, 2) and the ortho-NH3 (3, 3) and (6, 6) inversion lines. Six major complexes of dense ammonia are identified, three of them on either side of the starburst center, out to projected galactocentric radii of ~250 pc. Rotational temperatures are derived toward selected individual positions, as well as for the entire southeastern and northwestern molecular complexes. The application of radiative transfer large velocity gradient models reveals that the bulk of the ammonia molecules is embedded in a one-temperature gas phase. Kinetic temperatures of this gas are ~200 and 140 K toward the southwest and northeast, respectively. The temperatures under which ammonia was formed in the past are with 30 K also warmer toward the southwest than toward the northeast (~15-20 K). This is indicated by the ortho-ammonia-to-para-ammonia ratio, which is ~1 and 1.5-2.5 toward the southwest and northeast, respectively. Ammonia column densities in the brightest complexes are in the range of (6-11) × 1014 cm-2, which adds up to a total ammonia mass of ~20 M☉, about evenly distributed toward both sides of the nucleus. Ammonia abundances relative to H2 are ~3 × 10-8. In the southwestern complex, the ammonia abundances increase from the starburst center to larger galactocentric radii. Toward the center of NGC 253, NH3 (1, 1), (2, 2), and (6, 6) are detected in absorption against an unresolved continuum source. At the same location, however, ammonia (3, 3) is found in emission, which indicates maser activity. This would be the first detected extragalactic NH3 maser. Evidence for an expanding shell in the southwestern complex is provided. The shell, with a dynamical age of ~1.3 Myr, is centered on an X-ray point source that must be located within the dense gas of NGC 253. The shell and X-ray properties can be reproduced by the energy input of a highly obscured young stellar cluster with a mass of ~105 M☉, which also heats the dense gas. A current star formation rate of ~2.8 M☉ yr-1 is derived for the nuclear starburst in NGC 253 based on its 1.2 cm continuum emission.

AN EXTRAGALACTIC 12CO J = 3-2 SURVEY WITH THE HEINRICH HERTZ TELESCOPE

We present results of a {sup 12}CO J = 3-2 survey of 125 nearby galaxies obtained with the 10 m Heinrich Hertz Telescope, with the aim to characterize the properties of warm and dense molecular gas in a large variety of environments. With an angular resolution of 22, {sup 12}CO 3-2 emission was detected in 114 targets. Based on 61 galaxies observed with equal beam sizes the {sup 12}CO 3-2/1-0 integrated line intensity ratio R{sub 31} is found to vary from 0.2 to 1.9, with an average value of 0.81. No correlations are found for R{sub 31} to Hubble-type and far-infrared luminosity. Possible indications for a correlation with inclination angle and the 60 {mu}m/100 {mu}m color temperature of the dust are not significant. Higher R{sub 31} ratios than in normal galaxies, hinting at enhanced molecular excitation, may be found in galaxies hosting active galactic nuclei. Even higher average values are determined for galaxies with bars or starbursts, the latter being identified by the ratio of infrared luminosity versus isophotal area, log [(L{sub FIR}/L{sub sun})/(D {sup 2}{sub 25}/kpc{sup 2})] > 7.25. (U)LIRGs are found to have the highest averaged R{sub 31} value. This may be a consequence of particularly vigorous starmorexa0» formation activity, triggered by galaxy interaction and merger events. The nuclear CO luminosities are slightly sublinearly correlated with the global FIR luminosity in both the {sup 12}CO J = 3-2 and the 1-0 lines. The slope of the log-log plots rises with compactness of the respective galaxy sub-sample, indicating a higher average density and a larger fraction of thermalized gas in distant luminous galaxies. While linear or sublinear correlations for the {sup 12}CO J = 3-2 line can be explained, if the bulk of the observed J = 3-2 emission originates from the molecular gas with densities below the critical one, the case of the {sup 12}CO J = 1-0 line with its small critical density remains a puzzle.«xa0less

The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9

Based on measurements with the Effelsberg 100-m telescope, a multi-line study of molecular species is presented toward the gravitational lens system PKS 1830-211, which is by far the best known target to study dense cool gas in absorption at intermediate redshift. Determining average radial velocities and performing Large Velocity Gradient radiative transfer calculations, the aims of this study are (1) to determine the density of the gas, (2) to constrain the temperature of the cosmic microwave background (CMB), and (3) to evaluate the proton-to-electron mass ratio at redshift z ˜ 0.89. Analyzing data from six rotational HC3N transitions (this includes the J=7≤ftarrow6 line, which is likely detected for the first time in the interstellar medium) we obtain n(H2) ~ 2600 cm-3 for the gas density of the south-western absorption component, assuming a background source covering factor, which is independent of frequency. With a possibly more realistic frequency dependence proportional to ν0.5 (the maximal exponent permitted by observational boundary conditions), n(H2) ~ 1700 cm-3. Again toward the south-western source, excitation temperatures of molecular species with optically thin lines and higher rotational constants are, on average, consistent with the expected temperature of the cosmic microwave background, T_CMB = 5.14 K. However, individually, there is a surprisingly large scatter which far surpasses expected uncertainties. A comparison of CS J =1 ≤ftarrow0 and 4≤ftarrow3 optical depths toward the weaker north-western absorption component results in T_ex = 11 K and a 1-σ error of 3 K. For the main component, a comparison of velocities determined from ten optically thin NH3 inversion lines with those from five optically thin rotational transitions of HC3N, observed at similar frequencies, constrains potential variations of the proton-to-electron mass ratio μ to Δμ / μ < 1.4 × 10 -6 with 3-σ confidence. Also including optically thin rotational lines from other molecular species, it is emphasized that systematic errors are Δ V < 1 km s-1, corresponding to Δμ/μ< 1.0× 10-6.

Molecular line mapping of the giant molecular cloud associated with RCW 106 – III. Multimolecular line mapping

We present multimolecular line maps obtained with the Mopra telescope towards the southern giant molecular cloud (GMC) complex G333, associated with the H ii region RCW 106. We have characterized the GMC by decomposing the 3D data cubes with gaussclumps, and investigated spatial correlations among different molecules with principal component analysis (PCA). We find no correlation between clump size and linewidth, but a strong correlation between emission luminosity and linewidth. PCA classifies molecules into high- and low-density tracers, and reveals that HCO+ and N2H+ are anticorrelated.

FORMALDEHYDE DENSITOMETRY OF STARBURST GALAXIES

With a goal toward deriving the physical conditions in external galaxies, we present a survey of the formaldehyde emission in a sample of starburst systems. By extending a technique used to derive the spatial density in star formation regions in our own Galaxy, we show how the relative intensity of the 110-111 and 211-212 K-doublet transitions of H2CO can provide an accurate densitometer for the active star formation environments found in starburst galaxies. Relying on an assumed kinetic temperature and cospatial emission and absorption from both H2CO transitions, our technique is applied to a sample of 19 infrared-bright galaxies which exhibit various forms of starburst activity. In the five galaxies of our sample where both H2CO transitions were detected, we have derived spatial densities. We also use H2CO to estimate the dense gas mass in our starburst galaxy sample, finding similar mass estimates for the dense gas-forming stars in these objects as derived using other dense gas tracers. A related trend can be seen when one compares LIR to our derived n(H2) for the five galaxies within which we have derived spatial densities. Even though our number statistics are small, there appears to be a trend toward higher spatial density for galaxies with higher infrared luminosity. This is likely another representation of the LIR-Mdense correlation.

Imaging the Molecular Gas Properties of a Major Merger Driving the Evolution of a z=2.5 Submillimeter Galaxy

We report the detection of spatially extended CO(J = 1→0) and CO(J = 5→4) emission in the z = 2.49 submillimeter galaxy (SMG) J123707+6214, using the Expanded Very Large Array and the Plateau de Bure Interferometer. The large molecular gas reservoir is spatially resolved into two CO(J = 1→0) components (northeast and southwest; previously identified in CO J = 3→2 emission) with respective gas masses of 4.3 and 3.5×10^(10) (α_(CO)/0.8) M_☉. We thus find that the optically invisible northeast component slightly dominates the gas mass in this system. The total molecular gas mass derived from the CO(J = 1→0) observations is ≳2.5× larger than estimated from CO(J = 3→2). The two components are at approximately the same redshift, but separated by ~20 kpc in projection. The morphology is consistent with that of an early-stage merger. The total amount of molecular gas is sufficient to maintain the intense 500 M_☉ yr^(–1) starburst in this system for at least ~160 Myr. We derive line brightness temperature ratios of r_(31) = 0.39 ± 0.09 and 0.37 ± 0.10, and r_(51) = 0.26 ± 0.07 and 0.25 ± 0.08 in the two components, respectively, suggesting that the J ≥ 3 lines are substantially subthermally excited. This also suggests comparable conditions for star formation in both components. Given the similar gas masses of both components, this is consistent with the comparable starburst strengths observed in the radio continuum emission. Our findings are consistent with other recent studies that find evidence for lower CO excitation in SMGs than in high-z quasar host galaxies with comparable gas masses. This may provide supporting evidence that both populations correspond to different evolutionary stages in the formation of massive galaxies.

First Detection of Ammonia in M82

We report the detection of the (J, K) = (1, 1), (2, 2), and (3, 3) inversion lines of ammonia (NH3) toward the southwestern molecular lobe in M82. The relative intensities of the ammonia lines are characterized by a rotational temperature of Trot = 29 ± 5 K, which implies an average kinetic temperature of Tkin ≈ 60 K. A Gaussian decomposition of the observed spectra indicates increasing kinetic temperatures toward the nucleus of M82, consistent with recent findings based on CO observations. The observations imply a very low NH3 abundance relative to H2, X(NH3) ≈ 5 × 10-10. We present evidence for a decreasing NH3 abundance toward the central active regions in M82 and interpret this abundance gradient in terms of photodissociation of NH3 in photodissociation regions. The low temperature derived here from NH3 also explains the apparent underabundance of complex molecules like CH3OH and HNCO, which has previously been reported.