arXiv subjects

Paul Martini

Publications and source records attributed to Paul Martini.

At least 163 records · Page 9Linked to original sources

arXiv2005

Spatially-Resolved Narrow Line Region Kinematics in Active Galactic Nuclei

We have analyzed HST spectroscopy of 24 nearby AGNs to investigate spatially-resolved gas kinematics in the Narrow Line Region (NLR). These observations effectively isolate the nuclear line profiles on less than 100 pc scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion sigma_* of the host galaxy, a quantity which relates with substantially less scatter to the mass of the central, supermassive black hole, and more generally characterize variations in the NLR velocity field with radius. We find that line widths measured with STIS at a range of spatial scales systematically underestimate both sigma_* and the line width measured from ground-based observations, although they do have comparably large scatter to the relation between ground-based NLR line width and sigma_*. There are no obvious trends in the residuals when compared with a range of host galaxy and nuclear properties. The widths and asymmetries of [OIII] 5007 and [SII] 6716, 6731 as a function of radius exhibit a wide range of behavior. Some of the most common phenomena are substantial width increases from the STIS to the large-scale, ground-based aperture and almost no change in line profile between the unresolved nuclear spectrum and ground-based measurements. We identify asymmetries in a surprisingly large fraction of low-ionization [SII] line profiles and several examples of substantial red asymmetries in both [OIII] and [SII]. These results underscore the complexity of the circumnuclear material that constitutes the NLR and suggest that the scatter in the NLR width and sigma_* correlation can not be substantially reduced with a simple set of empirical relations.

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arXiv2005

Black Holes in Galaxy Mergers: Evolution of Quasars

Based on numerical simulations of gas-rich galaxy mergers, we discuss a model in which quasar activity is tied to the self-regulated growth of supermassive black holes in galaxies. Nuclear inflow of gas attending a galaxy collision triggers a starburst and feeds black hole growth, but for most of the duration of the starburst, the black hole is heavily obscured by surrounding gas and dust which limits the visibility of the quasar, especially at optical and UV wavelengths. Eventually, feedback energy from accretion heats the gas and expels it in a powerful wind, leaving a 'dead quasar'. Between buried and dead phases there is a window during which the galaxy would be seen as a luminous quasar. Because the black hole mass, radiative output, and distribution of obscuring gas and dust all evolve strongly with time, the duration of this phase of observable quasar activity depends on both the waveband and imposed luminosity threshold. We determine the observed and intrinsic lifetimes as a function of luminosity and frequency, and calculate observable lifetimes ~10 Myr for bright quasars in the optical B-band, in good agreement with empirical estimates and much smaller than the black hole growth timescales ~100 Myr, naturally producing a substantial population of 'buried' quasars. However, observed and intrinsic energy outputs converge in the IR and hard X-ray bands as attenuation becomes weaker and chances of observation greatly increase. We obtain the distribution of column densities along sightlines in which the quasar is seen above a given luminosity, and find that our result agrees remarkably well with observed estimates of the column density distribution from the SDSS for appropriate luminosity thresholds. (Abridged)

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arXiv2005

A Physical Model for the Origin of Quasar Lifetimes

We propose a model of quasar lifetimes in which observational quasar lifetimes and an intrinsic lifetime of rapid accretion are strongly distinguished by the physics of obscuration by surrounding gas and dust. Quasars are powered by gas funneled to galaxy centers, but for a large part of the accretion lifetime are heavily obscured by the large gas densities powering accretion. In this phase, starbursts and black hole growth are fueled but the quasar is buried. Eventually, feedback from accretion energy disperses surrounding gas, creating a window in which the black hole is observable optically as a quasar, until accretion rates drop below those required to maintain a quasar luminosity. We model this process and measure the unobscured and intrinsic quasar lifetimes in a hydrodynamical simulation of a major galaxy merger. The source luminosity is determined from the black hole accretion rate, calculated from local gas properties. We calculate the column density of hydrogen to the source along multiple lines of sight and use these column densities and gas metallicities to determine B-band attenuation of the source. Defining the observable quasar lifetime as the total time with an observed B-band luminosity above some limit L_B,min, we find lifetimes ~10-20 Myr for L_B,min=10^11 L_sun (M_B=-23), in good agreement with observationally determined quasar lifetimes. This is significantly smaller than the intrinsic lifetime ~100 Myr obtained if attenuation is neglected. The ratio of observed to intrinsic lifetime is also strong function of both the limiting luminosity and the observed frequency.

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arXiv2004

Bars from the Inside Out: An HST Study of their Dusty Circumnuclear Regions

The results of bar-driven mass inflow are directly observable in high-resolution HST observations of their circumnuclear regions. These observations reveal a wealth of structures dominated by dust lanes, often with a spiral-like morphology, and recent star formation. Recent work has shown that some of these structures are correlated with the presence or absence of a bar. I extend this work with an investigation of circumnuclear morphology as a function of bar strength for a sample of 48 galaxies with both measured bar strengths and ``structure maps'' computed from HST images. The structure maps for these galaxies, which have projected spatial resolutions of 2 - 15 pc, show that the fraction of galaxies with grand-design (GD) circumnuclear dust spirals increases significantly with bar strength, while tightly wound dust spirals are only present in the most axisymmetric galaxies. GD structure is only found at the centers of galaxies classified as SB(s) or SB(rs) and not SB(r). SB(s) galaxies on average have stronger bars than SB(r) galaxies. There is also a modest increase in the fraction of loosely wound dust spirals at later morphological types, which may reflect an increase in the fraction of galaxies with circumnuclear, gaseous disks. (abridged)

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arXiv2004

PANIC: A Near-infrared Camera for the Magellan Telescopes

PANIC (Persson's Auxiliary Nasmyth Infrared Camera) is a near-infrared camera designed to operate at any one of the f/11 folded ports of the 6.5m Magellan telescopes at Las Campanas Observatory, Chile. The instrument is built around a simple, all-refractive design that reimages the Magellan focal plane to a plate scale of 0.125'' pixel^{-1} onto a Rockwell 1024x1024 HgCdTe detector. The design goals for PANIC included excellent image quality to sample the superb seeing measured with the Magellan telescopes, high throughput, a relatively short construction time, and low cost. PANIC has now been in regular operation for over one year and has proved to be highly reliable and produce excellent images. The best recorded image quality has been ~0.2'' FWHM.

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arXiv2004

Why does Low-Luminosity AGN Fueling Remain an Unsolved Problem?

Despite many years of effort, observational studies have not found a strong correlation between the presence of any proposed fueling mechanism and low-luminosity AGN. After a discussion of the mass requirements for fueling, I summarize this observational work and provide a number of hypotheses for why the nature of AGN fueling has remained unresolved. In particular, I stress the potential importance of the increasing number of candidate fueling mechanisms with decreasing mass accretion rate, the relevant spatial scales for different fueling mechanisms, and the lifetime of an individual episode of nuclear accretion. The episodic AGN lifetime is a particularly relevant complication if it is comparable to or shorter than the time that the responsible fueling mechanisms are observationally detectable. I conclude with a number of relatively accessible areas for future investigation.

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arXiv2004

A Population of Massive Globular Clusters in NGC 5128

We present velocity dispersion measurements of 14 globular clusters in NGC 5128 (Centarus A) obtained with the MIKE echelle spectrograph on the 6.5m Magellan Clay telescope. These clusters are among the most luminous globular clusters in NGC 5128 and have velocity dispersions comparable to the most massive clusters known in the Local Group, ranging from 10 - 30 km/s. We describe in detail our cross-correlation measurements, as well as simulations to quantify the uncertainties. These 14 globular clusters are the brightest NGC 5128 globular clusters with surface photometry and structural parameters measured from the Hubble Space Telescope. We have used these measurements to derive masses and mass-to-light ratios for all of these clusters and establish that the fundamental plane relations for globular clusters extend to an order of magnitude higher mass than in the Local Group. The mean mass-to-light ratio for the NGC 5128 clusters is ~3+/-1, higher than measurements for all but the most massive Local Group clusters. These massive clusters begin to bridge the mass gap between the most massive star clusters and the lowest-mass galaxies. We find that the properties of NGC 5128 globular clusters overlap quite well with the central properties of nucleated dwarf galaxies and ultracompact dwarf galaxies. As six of these clusters also show evidence for extratidal light, we hypothesize that at least some of these massive clusters are the nuclei of tidally stripped dwarfs.

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arXiv2003

Multiepoch Sky Surveys and the Lifetime of Quasars

We present a new method to measure the episodic lifetime of quasars with current and future large-scale sky surveys. Future photometric observations of large samples of confirmed quasars can provide a direct measurement (or interesting lower limit) to the lifetime of an individual episode of quasar activity (t_Q) and potentially enable the study of post-quasar host galaxies. Photometric observations of the quasars found by the Sloan Digital Sky Survey (SDSS) and 2dF Survey could, with a time baseline of ten years, determine t_Q to within a factor of two if t_Q < 10^5 years, or set a lower limit to the quasar lifetime. Multiple-epoch, precise photometry with the proposed Large Synoptic Survey Telescope could test more complex models for quasar variability and mean quasar luminosity evolution. These observations could also constrain the rate that tidal disruptions of single stars produce quasar luminosities. It is possible to reverse the order of this investigation; previous-epoch plate material, such as the Digitized Sky Survey, can be used to determine if any of the SDSS quasars had not yet turned on at the time of these prior observations. Measurements of the entire SDSS quasar sample over the ~50 year baseline provided by these plates can potentially be used to estimate t_Q to within a factor of two if t_Q < 10^{5.5} years, provided quasar variability can be accurately characterized and the detection efficiency and photometric calibration of the plate material can be well determined. These measurements of t_Q will have comparable quality to existing, more indirect estimates of the quasar lifetime. Analysis of the 3814 quasars in the SDSS Early Data Release finds that t_Q must be larger than approximately 20,000 years.

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arXiv2003

QSO Lifetimes

The QSO lifetime t_Q is one of the most fundamental quantities for understanding black hole and QSO evolution, yet it remains uncertain by several orders of magnitude. If t_Q is long, then only a small fraction of galaxies went through a luminous QSO phase. In contrast, a short lifetime would require most galaxies today to have undergone a QSO phase in their youth. The current best estimates or constraints on t_Q from black hole demographics and the radiative properties of QSOs vary from at least 10^6 to 10^8 years. This broad range still allows both possibilities: that QSOs were either a rare or a common stage of galaxy evolution. These constraints also do not rule out the possibility that QSO activity is episodic, with individual active periods much shorter than the total active lifetime. In the next few years a variety of additional observational constraints on the lifetimes of QSOs will become available, including clustering measurements and the proximity effect. These new constraints can potentially determine t_Q to within a factor of 3 and therefore answer one of the most fundamental questions in black hole evolution: Do they shine as they grow? This precision will also test the viability of our current model for accretion physics, specifically the radiative efficiency and need for super-Eddington luminosities to explain the black hole population.

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arXiv2002

Circumnuclear Dust in Nearby Active and Inactive Galaxies. I. Data

The detailed morphology of the interstellar medium (ISM) in the central kiloparsec of galaxies is controlled by pressure and gravitation. The combination of these forces shapes both circumnuclear star formation and the growth of the central, supermassive black hole. We present visible and near-infrared Hubble Space Telescope images and color maps of 123 nearby galaxies that show the distribution of the cold ISM, as traced by dust, with excellent spatial resolution. These observations reveal that nuclear dust spirals are found in the majority of active and inactive galaxies and they possess a wide range in coherence, symmetry, and pitch angle. We have used this large sample to develop a classification system for circumnuclear dust structures. In spite of the heterogeneous nature of the complete sample, we only find symmetric, two-arm nuclear dust spirals in galaxies with large scale bars and these dust lanes clearly connect to dust lanes along the leading edges of the large scale bars. Not all dust lanes along large scale bars form two arm spirals, however, and several instead end in nuclear rings. We find that tightly wound, or low pitch angle, nuclear dust spirals are more common in unbarred galaxies than barred galaxies. Finally, the extended narrow line region in several of the active galaxies is well-resolved. The connection between the ionized gas and circumnuclear dust lanes in four of these galaxies provides additional evidence that a significant fraction of their extended narrow line region is ambient gas photoionized in situ by the active nucleus. In a future paper, we will use our classification system for circumnuclear dust to identify differences between active and inactive galaxies, as well as barred and unbarred galaxies, in well-matched subsamples of these data.

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arXiv2002

Circumnuclear Dust in Nearby Active and Inactive Galaxies. II. Bars, Nuclear Spirals, and the Fueling of Active Galactic Nuclei

(Abridged) We present a detailed study of the relation between circumnuclear dust morphology, host galaxy properties, and nuclear activity in nearby galaxies. We use our sample of 123 nearby galaxies with visible--near-infrared colormaps from the Hubble Space Telescope to create well-matched, "paired" samples of 28 active and 28 inactive galaxies, as well as 19 barred and 19 unbarred galaxies, that have the same host galaxy properties. Comparison of the barred and unbarred galaxies shows that grand design nuclear dust spirals are only found in galaxies with a large-scale bar. Tightly wound nuclear dust spirals, in contrast, show a strong tendency to avoid galaxies with large-scale bars. Comparison of the AGN and inactive samples shows that nuclear dust spirals, which may trace shocks and angular momentum dissipation in the ISM, occur with comparable frequency in both active and inactive galaxies. The only difference between the active and inactive galaxies is that several inactive galaxies appear to completely lack dust structure in their circumnuclear region, while none of the AGN lack this structure. The comparable frequency of nuclear spirals in active and inactive galaxies, combined with previous work that finds no significant differences in the frequency of bars or interactions between well-matched active and inactive galaxies, suggests that no universal fueling mechanism for low-luminosity AGN operates at spatial scales greater than ~100 pc radius from the galactic nuclei. The similarities instead suggest that the lifetime of nuclear activity is less than the characteristic inflow time from these spatial scales. An order-of-magnitude estimate of this inflow time is the dynamical timescale. This sets an upper limit of several million years to the lifetime of an individual episode of nuclear activity.

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arXiv2002

An Unexpectedly High AGN Fraction in Red Cluster Galaxies

As part of a program to study the evolution of active galactic nuclei (AGN) in clusters of galaxies, we present our results for Abell 2104. A deep Chandra observation of this massive, z = 0.154 cluster reveals a significant X-ray point source excess over the expectations of blank fields, including eight X-ray counterparts with R<20 mag. Our spectroscopy shows that all six X-ray sources associated with red counterparts are cluster members and their X-ray properties are consistent with all of them being AGN. Only one of the six has the emission lines characteristic of optically selected AGN; the remaining five would not have been classified as AGN based on their optical spectra. This suggests the existence of a large population of obscured, or at least optically unremarkable, AGN in clusters of galaxies. These six sources correspond to a lower limit of ~5% of the AGN fraction in cluster galaxies with R<20 mag (rest-frame M_V = -19.5 mag) and is comparable to the blue galaxy fraction in the cluster. Such an obscured AGN population in clusters of galaxies has many implications for cluster galaxy evolution, the hidden growth of their central, supermassive black holes, estimates of the star formation rate at infrared and radio wavelengths, and the observed variance in the hard X-ray background.

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arXiv2002

Hubble Space Telescope Imaging of the Circumnuclear Environments of the CfA Seyfert Galaxies: Nuclear Spirals and Fueling

We present archival Hubble Space Telescope images of the nuclear regions of 43 of the 46 Seyfert galaxies found in the volume-limited, spectroscopically-complete CfA Redshift Survey sample. Using an improved method of image contrast enhancement, we create detailed high-quality structure maps that allow us to study the distributions of dust, star clusters, and emission-line gas in the circumnuclear regions (100-1000 pc scales) and in the associated host galaxy. Essentially all of these Seyfert galaxies have circumnuclear dust structures with morphologies ranging from grand-design two-armed spirals to chaotic dusty disks. In most Seyferts there is a clear physical connection between the nuclear dust spirals on hundreds of parsec scales and large-scale bars and spiral arms in the host galaxies proper. These connections are particularly striking in the interacting and barred galaxies. Such structures are predicted by numerical simulations of gas flows in barred and interacting galaxies, and may be related to the fueling of AGN by matter inflow from the host galaxy disks. We see no significant differences in the circumnuclear dust morphologies of Seyfert 1s and 2s, and very few Seyfert 2 nuclei are obscured by large-scale dust structures in the host galaxies. If Seyfert 2s are obscured Seyfert 1s, then the obscuration must occur on smaller scales than those probed by HST.

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arXiv2001

Very Red and Extremely Red Galaxies in the Fields of z ~ 1.5 Radio-Loud Quasars

We previously identified an excess of mostly red galaxies around 31 RLQs at z=1-2. These fields have an ERO (extremely red object, R-K>6) density 2.7 times higher than the field. Assuming the EROs are passively evolved galaxies at the quasar redshifts, they have characteristic luminosities of only ~L^*. We also present new observations of four z~1.54 RLQ fields: (1) Wide-field J & Ks data confirm an Abell richness ~2 excess within 140" of Q0835+580 but an excess only within 50" of Q1126+101. (2) In 3 fields we present deep narrow-band redshifted H-alpha observations. We detect five candidate galaxies at the quasar redshifts, a surface density 2.5x higher than the field. (3) SCUBA sub-mm observations of 3 fields detect 2 quasars and 2 galaxies with SEDs best fit as highly reddened galaxies at the quasar z. (4) H-band adaptive optics (AO) imaging is used to estimate redshifts for 2 red, bulge-dominated galaxies using the Kormendy relation. Both have structural redshifts foreground to the quasar, but these are not confirmed by photometric redshifts, possibly because their optical photometry is corrupted by scattered light from the AO guidestar. (5) We use quantitative SED fits to constrain the photometric redshifts z_ph for some galaxies. Most galaxies near Q0835+580 are consistent with being at its redshift, including a candidate very old passively evolving galaxy. Many very & extremely red objects have z_ph z_q, and dust reddening is required to fit most of them, including many objects whose fits also require relatively old stellar populations. Large reddenings of E(B-V)~0.6 are required to fit four J-K selected EROs, though all but one of them have best-fit z_ph>z_q. These objects may represent a population of dusty high-z galaxies underrepresented in optically selected samples. (Abridged)

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arXiv2001

Hubble Space Telescope Observations of the CfA Seyfert 2s: Near-infrared Surface Photometry and Nuclear Bars

We present near-infrared J and H surface photometry of 24 of the nearby Seyfert 1.8, 1.9 and 2 galaxies from the CfA Seyfert sample. The excellent angular resolution of HST probes spatial scales as small as tens of parsecs in most of these AGN and is sensitive to the presence of nuclear bars and other potential signatures of the AGN fueling process that channels host galaxy gas and dust to the nuclear region. We have used elliptical isophote techniques to search for nuclear bars in all of these galaxies and have employed a two-dimensional fitting technique to model the nuclear point source and surface brightness distribution of a bright subsample of these galaxies in an attempt to alleviate the impact of the nuclear point source on our sensitivity to nuclear bars. We find stellar nuclear bar candidates in four of these galaxies: Mrk 471, Mrk 270, Mrk 573, and NGC 5929, nearly 20% of the total sample. The percentage rises to ~30% when systems with disturbed morphologies or high inclinations are excluded. The nuclear bars in Mrk 573 and Mrk 270 exhibit some evidence for dust lanes along their leading edges, analogous to the structures seen in host galaxy bars, while the dust lanes in Mrk 471 and NGC 5929 exhibit a more complex morphology. The fact that most of these AGN do not appear to contain stellar nuclear bars suggests that they are not the fueling mechanism for most low-luminosity AGN.

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arXiv2001

Morphology of AGN in the central kiloparsec

Hubble Space Telescope observations of the central kiloparsec of AGN have revealed a wealth of structure, particularly nuclear bars and spirals, that are distinct from analogous features in the disks of spiral galaxies. WFPC2 and NICMOS images of a large sample of AGN observed at high spatial resolution make it possible to quantify the frequency and detailed properties of these structures. Nearly all AGN have nuclear spiral dust lanes in the central kiloparsec, while only a small minority contain nuclear bars. If these nuclear dust spirals trace shocks in the circumnuclear, gaseous disks, they may dissipate sufficient angular momentum to fuel the active nucleus.

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arXiv2001

A Deep Multicolor Survey. VII. Extremely Red Objects and Galaxy Formation

Extremely Red Objects (EROs) offer a window to the universe at z~1 analogous to that provided by the Lyman Break galaxies at z=3. Passive evolution and hierarchical galaxy formation models make very distinct predictions for the K (2.2um) surface density of galaxies at z~1 and EROs are a powerful constraint on these theories. I present a study of nine resolved EROs with R-K>5.3 and K<18 mag found in the 185 arcmin^2 of the Deep Multicolor Survey with near-infrared imaging. Photometric redshifts for these galaxies shows they all lie at z=0.8-1.3. The relatively blue J-K colors of these galaxies suggest that most are old ellipticals, rather than dusty starbursts. The surface density of EROs in this survey (>0.05 arcmin^-2), which is a lower limit to the total z~1 galaxy surface density, is an order of magnitude below the prediction of passive galaxy evolution, yet over a factor of two higher than the hierarchical galaxy formation prediction for a flat, matter-dominated universe. A flat, Lambda-dominated universe may bring the hierarchical galaxy formation model into agreement with the observed ERO surface density.

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arXiv2000

Quasar Clustering and the Lifetime of Quasars

Although the population of luminous quasars rises and falls over a period of 10^9 years, the typical lifetime of individual quasars is uncertain by several orders of magnitude. We show that quasar clustering measurements can substantially narrow the range of possible lifetimes with the assumption that luminous quasars reside in the most massive host halos. If quasars are long-lived, then they are rare phenomena that are highly biased with respect to the underlying dark matter, while if they are short-lived they reside in more typical halos that are less strongly clustered. For a given quasar lifetime, we calculate the minimum host halo mass by matching the observed space density of quasars, using the Press-Schechter approximation. We use the results of Mo & White to calculate the clustering of these halos, and hence of the quasars they contain, as a function of quasar lifetime. A lifetime of t_Q = 4 x 10^7 years, the e-folding timescale of an Eddington luminosity black hole with accretion efficiency eps=0.1, corresponds to a quasar correlation length r_0 ~ 10 Mpc/h in low-density cosmological models at z=2-3; this value is consistent with current clustering measurements, but these have large uncertainties. High-precision clustering measurements from the 2dF and Sloan quasar surveys will test our key assumption of a tight correlation between quasar luminosity and host halo mass, and if this assumption holds then they should determine t_Q to a factor of three or better. An accurate determination of the quasar lifetime will show whether supermassive black holes acquire most of their mass during high-luminosity accretion, and it will show whether the black holes in the nuclei of typical nearby galaxies were once the central engines of high-luminosity quasars.

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