arXiv subjects

Matthew A. Malkan

Publications and source records attributed to Matthew A. Malkan.

At least 163 records · Page 9Linked to original sources

arXiv2010

The Lick AGN Monitoring Project: Alternate Routes to a Broad-line Region Radius

It is now possible to estimate black hole masses across cosmic time, using broad emission lines in active galaxies. This technique informs our views of how galaxies and their central black holes coevolve. Unfortunately, there are many outstanding uncertainties associated with these "virial" mass estimates. One of these comes from using the accretion luminosity to infer a size for the broad-line region. Incorporating the new sample of low-luminosity active galaxies from our recent monitoring campaign at Lick Observatory, we recalibrate the radius-luminosity relation with tracers of the accretion luminosity other than the optical continuum. We find that the radius of the broad-line region scales as the square root of the X-ray and Hbeta luminosities, in agreement with recent optical studies. On the other hand, the scaling appears to be marginally steeper with narrow-line luminosities. This is consistent with a previously observed decrease in the ratio of narrow-line to X-ray luminosity with increasing total luminosity. The radius of the broad-line region correlates most tightly with Hbeta luminosity, while the X-ray and narrow-line relations both have comparable scatter of a factor of two. These correlations provide useful alternative virial BH masses in objects with no detectable optical/UV continuum emission, such as high-redshift galaxies with broad emission lines, radio-loud objects, or local active galaxies with galaxy-dominated continua.

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arXiv2010

Overdensity of i'-Dropout Galaxies in the Subaru Deep Field: A Candidate Protocluster at z ~ 6

We investigate the sky distribution of z ~ 6 Lyman break galaxies selected as i'-dropouts having i' - z' > 1.45 down to z' < 26.5 in the Subaru Deep Field (SDF). We discover 37 i'-dropouts clustered in a projected comoving 21.6 x 21.6 Mpc^2 region at z = 6, showing a local density excess. Carrying out follow-up spectroscopy, we identify four of them as Lyman-alpha emitters at z = 5.92, 6.01, 6.03 and 6.03 (spread over a distance of 46.6 Mpc). The number density of the cluster itself in SDF is ~ 2.2 x 10^{-7} Mpc^{-3}, smaller than those of protoclusters (i.e., forming galaxy clusters) at z ~ 2-5.7. Also, the structure shows ~4-21 times larger galaxy number density than those of z ~ 6 galaxies in a general field. It has a mass of M ~ 1.5^{+1.8}_{-0.5} x 10^{15}M_sun, comparable to those of z ~ 0-5 protoclusters. Since the contamination of our sample by interlopers is estimated to be quite low, 5.9%, most of the other unconfirmed i'-dropouts in the overdense region can be also z ~ 6 galaxies. Hence, it could be a candidate forming cluster at z ~ 6, representing a progenitor of galaxy clusters seen in the recent-day Universe.

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arXiv2010

Spitzer Space Telescope Constraint on the Stellar Mass of a z = 6.96 Lyman Alpha Emitter

We obtained mid-infrared 3.6 and 4.5 micron imaging of a z=6.96 Lyman alpha emitter (LAE) IOK-1 discovered in the Subaru Deep Field, using Spitzer Space Telescope Infrared Array Camera observations. After removal of a nearby bright source, we find that IOK-1 is not significantly detected in any of these infrared bands to m_3.6 ~ 24.00 and m_4.5 ~ 23.54 at 3 sigma. Fitting population synthesis models to the spectral energy distribution consisting of the upper limit fluxes of the optical to infrared non-detection images and fluxes in detection images, we constrain the stellar mass M* of IOK-1. This LAE could have either a mass as low as M* <~ 2-9 x 10^8 Msun for the young age (<~ 10 Myr) and the low dust reddening (A_V ~ 0) or a mass as large as M* <~ 1-4 x 10^{10} Msun for either the old age (> 100 Myr) or the high dust reddening (A_V ~ 1.5). This would be within the range of masses of z ~ 3-6.6 LAEs studied to date, ~ 10^6-10^{10} Msun. Hence, IOK-1 is not a particularly unique galaxy with extremely high mass or low mass but is similar to one of the LAEs seen at the later epochs.

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arXiv2010

The Lick AGN Monitoring Project: Velocity-Delay Maps from the Maximum-Entropy Method for Arp 151

We present velocity-delay maps for optical H I, He I, and He II recombination lines in Arp 151, recovered by fitting a reverberation model to spectrophotometric monitoring data using the maximum-entropy method. H I response is detected over the range 0-15 days, with the response confined within the virial envelope. The Balmer-line maps have similar morphologies but exhibit radial stratification, with progressively longer delays for Hgamma to Hbeta to Halpha. The He I and He II response is confined within 1-2 days. There is a deficit of prompt response in the Balmer-line cores but strong prompt response in the red wings. Comparison with simple models identifies two classes that reproduce these features: freefalling gas, and a half-illuminated disk with a hotspot at small radius on the receding lune. Symmetrically illuminated models with gas orbiting in an inclined disk or an isotropic distribution of randomly inclined circular orbits can reproduce the virial structure but not the observed asymmetry. Radial outflows are also largely ruled out by the observed asymmetry. A warped-disk geometry provides a physically plausible mechanism for the asymmetric illumination and hotspot features. Simple estimates show that a disk in the broad-line region of Arp 151 could be unstable to warping induced by radiation pressure. Our results demonstrate the potential power of detailed modeling combined with monitoring campaigns at higher cadence to characterize the gas kinematics and physical processes that give rise to the broad emission lines in active galactic nuclei.

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arXiv2010

The Lick AGN Monitoring Project: Reverberation Mapping of Optical Hydrogen and Helium Recombination Lines

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7M_sun and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hbeta emission, which we have previously reported. We present here the light curves for the Halpha, Hgamma, HeII 4686, and HeI 5876 emission lines and the time lags for the emission-line responses relative to changes in the continuum flux. Combining each emission-line time lag with the measured width of the line in the variable part of the spectrum, we determine a virial mass of the central supermassive black hole from several independent emission lines. We find that the masses are generally consistent within the uncertainties. The time-lag response as a function of velocity across the Balmer line profiles is examined for six of the AGNs. Finally we compare several trends seen in the dataset against the predictions from photoionization calculations as presented by Korista & Goad. We confirm several of their predictions, including an increase in responsivity and a decrease in the mean time lag as the excitation and ionization level for the species increases. Further confirmation of photoionization predictions for broad-line gas behavior will require additional monitoring programs for these AGNs while they are in different luminosity states. [abridged]

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arXiv2010

The Lick AGN Monitoring Project: The MBH - sigma Relation For Reverberation-Mapped Active Galaxies

(Abridged) To investigate the black hole mass (MBH) vs. stellar velocity dispersion relation of active galaxies, we measured the velocity dispersions of a sample of local Seyfert 1 galaxies, for which we have recently determined MBH using reverberation mapping. For most objects, velocity dispersions were measured from high S/N ratio optical spectra centered on the Ca II triplet region (~8500 A), obtained at the Keck, Palomar, and Lick Observatories. For two objects, in which the Ca II triplet region was contaminated by nuclear emission, the measurement was based on high-quality H-band spectra obtained with the OSIRIS at the Keck-II Telescope. Combining our new measurements with data from the literature, we assemble a sample of 24 active galaxies with stellar velocity dispersions and reverberation-based MBH measurements in the range of black hole mass 10^6<MBH/M_sun<10^9. We use this sample to obtain reverberation mapping constraints on the slope and intrinsic scatter of the M-sigma relation of active galaxies. Assuming a constant virial coefficient f for the reverberation mapping black hole masses, we find a slope b=3.55+-0.60 and the intrinsic scatter sigma_int=0.43+-0.08 dex in the relation log (MBH/M_sun) = a + b log (sigma/200 km/s), which are consistent with those found for quiescent galaxies. We derive an updated value of the virial coefficient f by finding the value which places the reverberation masses in best agreement with the M-sigma relation of quiescent galaxies; using the quiescent M-sigma relation determined by Gultekin et al. we find log f=0.72^{+0.09-0.10} with an intrinsic scatter of 0.44+-0.07 dex. The uncertainty of the virial coefficient remains one of the main sources of the uncertainty in black hole mass determinations using reverberation mapping, and therefore also in single-epoch spectroscopic estimates of MBH in active galaxies.

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arXiv2009

Cosmic Evolution of Black Holes and Spheroids. IV. The BH Mass - Spheroid Luminosity Relation

From high-resolution images of 23 Seyfert-1 galaxies at z=0.36 and z=0.57 obtained with the Near Infrared Camera and Multi-Object Spectrometer on board the Hubble Space Telescope (HST), we determine host-galaxy morphology, nuclear luminosity, total host-galaxy luminosity and spheroid luminosity. Keck spectroscopy is used to estimate black hole mass (M_BH). We study the cosmic evolution of the M_BH-spheroid luminosity (L_sph) relation. In combination with our previous work, totaling 40 Seyfert-1 galaxies, the covered range in BH mass is substantially increased, allowing us to determine for the first time intrinsic scatter and correct evolutionary trends for selection effects. We re-analyze archival HST images of 19 local reverberation-mapped active galaxies to match the procedure adopted at intermediate redshift. Correcting spheroid luminosity for passive luminosity evolution and taking into account selection effects, we determine that at fixed present-day V-band spheroid luminosity, M_BH/L_sph \propto (1+z)^(2.8+/-1.2). When including a sample of 44 quasars out to z=4.5 taken from the literature, with luminosity and BH mass corrected to a self-consistent calibration, we extend the BH mass range to over two orders of magnitude, resulting in M_BH/L_sph \propto (1+z)^(1.4+/-0.2). The intrinsic scatter of the relation, assumed constant with redshift, is 0.3+/-0.1 dex (<0.6 dex at 95% CL). The evolutionary trend suggests that BH growth precedes spheroid assembly. Interestingly, the M_BH-total host-galaxy luminosity relation is apparently non-evolving. It hints at either a more fundamental relation or that the spheroid grows by a redistribution of stars. However, the high-z sample does not follow this relation, indicating that major mergers may play the dominant role in growing spheroids above z~1.

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arXiv2009

Spitzer-IRS high resolution spectroscopic survey of the 12 micron Seyfert galaxies: II. Results for the Complete Dataset

We present the Spitzer 10-37um IRS high resolution (R~600) spectroscopic survey of the Seyfert galaxies of the 12 micron Galaxy Sample. The new spectra of 61 galaxies, with those already published, gives us a total of 91 12micron Seyfert galaxies observed, out of 112. We use an improved AGN classification for Seyfert galaxies: instead of the type 1 and 2 classes, we use the spectropolarimetric data to divide them into "AGN 1" and "AGN 2", where AGN 1's include all broad-line objects, including the Seyfert 2's showing hidden broad lines in polarized light, while AGN 2's contains only Seyferts with no detectable broad lines at all. We present various mid-IR observables and we find that these properties characterize the AGN 1's objects as a single family, with strongly AGN-dominated spectra. In contrast, the AGN 2's can be divided in two groups, the first one with properties similar to the AGN 1's and the second similar to the non-Seyfert galaxies, such as LINERs or starburst galaxies. We computed a semianalytical model to estimate the AGN and the starburst contributions to the mid-IR galaxy emission at 19um. We find that AGN 1 have an AGN contribution >73% and AGN 2 >45% of their total emission at 19um. The detection of [NeV] lines is an almost perfect signature of energy production by an AGN. We present mean spectra of the various AGN categories. We derive the first local luminosity functions for the mid-infrared lines and the PAH feature. No statistical difference is found in the space densities for Seyfert 1's and 2's, nor for the new classes of AGN 1's and 2's. The global output of accretion-powered galactic nuclei in the local universe is derived from the correlation between [NeV] line and the nonstellar IR continuum luminosity.

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arXiv2009

The Lick AGN Monitoring Project: Photometric Light Curves and Optical Variability Characteristics

The Lick AGN Monitoring Project targeted 13 nearby Seyfert 1 galaxies with the intent of measuring the masses of their central black holes using reverberation mapping. The sample includes 12 galaxies selected to have black holes with masses roughly in the range 10^6-10^7 solar masses, as well as the well-studied AGN NGC 5548. In conjunction with a spectroscopic monitoring campaign, we obtained broad-band B and V images on most nights from 2008 February through 2008 May. The imaging observations were carried out by four telescopes: the 0.76-m Katzman Automatic Imaging Telescope (KAIT), the 2-m Multicolor Active Galactic Nuclei Monitoring (MAGNUM) telescope, the Palomar 60-in (1.5-m) telescope, and the 0.80-m Tenagra II telescope. Having well-sampled light curves over the course of a few months is useful for obtaining the broad-line reverberation lag and black hole mass, and also allows us to examine the characteristics of the continuum variability. In this paper, we discuss the observational methods and the photometric measurements, and present the AGN continuum light curves. We measure various variability characteristics of each of the light curves. We do not detect any evidence for a time lag between the B- and V-band variations, and we do not find significant color variations for the AGNs in our sample.

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arXiv2009

The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7 M_sun and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hbeta emission. We present here the light curves for the objects in this sample and the subsequent Hbeta time lags for the nine objects where these measurements were possible. The Hbeta lag time is directly related to the size of the broad-line region, and by combining the lag time with the measured width of the Hbeta emission line in the variable part of the spectrum, we determine the virial mass of the central supermassive black hole in these nine AGNs. The absolute calibration of the black hole masses is based on the normalization derived by Onken et al. We also examine the time lag response as a function of velocity across the Hbeta line profile for six of the AGNs. The analysis of four leads to ambiguous results with relatively flat time lags as a function of velocity. However, SBS 1116+583A exhibits a symmetric time lag response around the line center reminiscent of simple models for circularly orbiting broad-line region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most easily explained by a simple gravitational infall model. Further investigation will be necessary to fully understand the constraints placed on physical models of the BLR by the velocity-resolved response in these objects.

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arXiv2009

Lyman Break Galaxies at z~1.8-2.8: GALEX/NUV Imaging of the Subaru Deep Field

Abridged: A photometric sample of ~7100 V<25.3 Lyman break galaxies (LBGs) has been selected by combining Subaru/Suprime-Cam BVRci'z' data with deep GALEX/NUV imaging of the Subaru Deep Field. Follow-up spectroscopy confirmed 24 LBGs at 1.5<z<2.7. Among the optical spectra, 12 have Ly-alpha emission with rest-frame equivalent widths of ~5-60AA. The success rate for identifying LBGs as NUV-dropouts at 1.5<z<2.7 is 86%. The rest-frame UV (1700AA) luminosity function (LF) is constructed from the photometric sample with corrections for stellar contamination and z<1.5 interlopers. The LF is 1.7+/-0.1 times higher than those of z~2 BXs and z~3 LBGs. Three explanations were considered, and it is argued that significantly underestimating low-z contamination or effective comoving volume is unlikely: the former would be inconsistent with the spectroscopic sample at 93% confidence, and the second explanation would not resolve the discrepancy. The third scenario is that different photometric selection of the samples yields non-identical galaxy populations, such that some BX galaxies are LBGs and vice versa. This argument is supported by a higher surface density of LBGs at all magnitudes while the redshift distribution of the two populations is nearly identical. This study, when combined with other star-formation rate (SFR) density UV measurements from LBG surveys, indicates that there is a rise in the SFR density: a factor of 3-6 (3-10) increase from z~5 (z~6) to z~2, followed by a decrease to z~0. This result, along with past sub-mm studies that find a peak at z~2 in their redshift distribution, suggest that z~2 is the epoch of peak star-formation. Additional spectroscopy is required to characterize the complete shape of the z~2 LBG UV LF via measurements of contamination and accurate distances.

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arXiv2009

Spitzer spectra of Seyfert galaxies

The Spitzer IRS high resolution spectra of about 90 Seyfert galaxies from the 12um Galaxy Sample are presented and discussed. These represent about 70% of the total complete sample of local Seyfert galaxies. The presence of starburst components in these galaxies can be quantified by powerful mid-IR diagnostics tools (i.e. 11.25um PAH feature equivalent width and the H_2 emission line intensity) as well as the AGN dominance can be measured by specific fine structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The observed line ratios are compared to the results of semianalytical models, which can be used to compute the AGN and starburst contributions to the total luminosity of the galaxies. The results are also discussed in the light of unification and evolution models.

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arXiv2009

AGN and starburst in bright Seyfert galaxies: from IR photometry to IR spectroscopy

Infrared photometry and later infrared spectroscopy provided powerful diagnostics to distinguish between the main emission mechanisms in galaxies: AGN and Starburst. After the pioneering work on infrared photometry with IRAS in the far-IR and the S.Pedro Martir and ESO ground-based work in the near-IR, ISO photometry extended up to 200um the coverage of the galaxies energy distributions. Then Spitzer collected accurate mid-infrared spectroscopy on different samples of galaxies. We will review the work done on the 12um galaxy sample since the times of IRAS photometry to the new Spitzer spectroscopy. The main results on the multifrequency data of 12um selected Seyfert galaxies are presented and discussed in the light of unification and evolution models. The spectroscopic work of Spitzer will soon be complemented at longer wavelengths by the Herschel spectrometers and in the future by SPICA at higher redshift.

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arXiv2008

First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7 M_sun. We present here the first results from this project -- the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hbeta lag measurement in this object of 4.25(+0.68/-0.66) days in the observed frame. Coupled with the width of the Hbeta emission line in the variable spectrum, we determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hbeta emission line which clearly shows infalling gas in the Hbeta-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.

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arXiv2008

Star Formation Rates and Metallicities of K-selected Star Forming Galaxies at z~2

We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K(AB)<23 in the Subaru Deep Field, for which Halpha and some other emission lines are detected in 0.9 to 2.3 micron spectra with a resolution of R=500. Using Halpha luminosities, we obtain star formation rates (SFRs), and then specific SFRs (SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have larger SFRs. A negative correlation is seen between stellar mass and SSFR, which is consistent with the previous results for z~2 galaxies. This implies that a larger growth of stellar mass occurs in less massive galaxies. In addition, gas-phase oxygen abundances, 12+log(O/H), are derived from the ratio of NII(lambda 6584) to Halpha using the N2 index method. We have found a correlation between stellar mass and oxygen abundance in the sense that more massive sBzKs tend to be more metal rich, which is qualitatively consistent with the relation for UV-selected z~2 galaxies. However, the metallicity of the sBzKs is ~0.2 dex higher than that of UV-selected galaxies with similar stellar masses, which is significant considering the small uncertainties. The sBzKs in our sample have redder R-K colors than the UV-selected galaxies. This galaxy color-dependence in the oxygen abundance may be caused by older or dustier galaxies having higher metallicities at z~2.

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arXiv2008

Late-time observations of SN2006gy: Still Going Strong

Owing to its extremely high luminosity and long duration, SN2006gy radiated more energy in visual light than any other known SN. Two hypotheses to explain its high luminosity -- that it was powered by shock interaction with CSM as implied by its Type IIn spectrum, or that it was fueled by radioactive decay from a large mass of 56Ni synthesized in a pair-instability SN -- predicted different late-time properties. Here we present observations of SN2006gy obtained more than a year after discovery. We were unable to detect it at visual wavelengths, but clear near-IR K and H-band detections show that it is still at least as luminous as the peak of a normal SN II. We also present spectra giving an upper limit to the late-time Ha luminosity of about 1e39 erg/s. Based on the weak late-time Ha, X-ray, and radio emission, combined with the difficulty of explaining the shift to IR wavelengths, we can rule out ongoing CSM interaction as the primary late-time power source. Instead, we propose that the evolution of SN2006gy is consistent with one of two possible scenarios: (1) A pair-instability SN plus modest CSM interaction, where the radioactive decay luminosity shifts to the IR because of dust formation. (2) An IR echo, where radiation emitted during peak luminosity heats a pre-existing dust shell at radii near 1 light year, requiring the progenitor star to have ejected another 10 Msun shell about 1500 yr before the SN.

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arXiv2008

A Lyman Break Galaxy Candidate at z~9

We report the discovery of a z~9 Lyman Break Galaxy (LBG) candidate, selected from the NICMOS Parallel Imaging Survey as a J-dropout with J110 - H160 = 1.7. Spitzer/IRAC photometry reveals that the galaxy has a blue H160 - 3.6 um color, and a spectral break between 3.6 and 4.5 um. We interpret this break as the Balmer break, and derive a best-fit photometric redshift of z~9. We use Monte Carlo simulations to test the significance of this photometric redshift, and show a 96% probability of z>7. We estimate a lower limit to the comoving number density of such galaxies at z~9 of phi > 3.8 x 10^{-6} Mpc^{-3}. If the high redshift of this galaxy is confirmed, this will indicate that the luminous end of the rest-frame UV luminosity function has not evolved substantially from z~ 9 to z~3. Still, some small degeneracy remains between this z~9 model and models at z~2-3; deep optical imaging (reaching I ~ 29 AB) can rule out the lower-z models.

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arXiv2007

Spitzer-IRS high resolution spectroscopy of the 12μm Seyfert galaxies: I. First results

The first high resolution Spitzer IRS 9-37um spectra of 29 Seyfert galaxies (about one quarter) of the 12um Active Galaxy Sample are presented and discussed. The high resolution spectroscopy was obtained with corresponding off-source observations. This allows excellent background subtraction, so that the continuum levels and strengths of weak emission lines are accurately measured. The result is several new combinations of emission line ratios, line/continuum and continuum/continuum ratios that turn out to be effective diagnostics of the strength of the AGN component in the IR emission of these galaxies. The line ratios [NeV]/[NeII], [OIV]/[NeII], already known, but also [NeIII]/[NeII] and [NeV]/[SiII] can all be effectively used to measure the dominance of the AGN. We extend the analysis, already done using the 6.2um PAH emission feature, to the equivalent width of the 11.25um PAH feature, which also anti-correlates with the dominance of the AGN. We measure that the 11.25um PAH feature has a constant ratio with the H_2 S(1) irrespective of Seyfert type, approximately 10 to 1. Using the ratio of accurate flux measurements at about 19um with the two spectrometer channels, having aperture areas differing by a factor 4, we measured the source extendness and correlated it with the emission line and PAH feature equivalent widths. The extendness of the source gives another measure of the AGN dominance and correlates both with the EWs of [NeII] and PAH emission. Using the rotational transitions of H$_2$ we were able to estimate temperatures (200-300K) and masses (1-10 x 10^6 M_sun), or significant limits on them, for the warm molecular component in the galaxies observed.

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