M. A. Malkan

Japan Aerospace Exploration Agency, Chōfu, Tōkyō, Japan

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Publications (272)725.08 Total impact

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    ABSTRACT: We analyse the 2-dimensional distribution and kinematics of the stars as well as molecular and ionised gas in the central few hundred parsecs of 5 active and 5 matched inactive galaxies. The equivalent widths of the Br-gamma line indicate there is no on-going star formation in their nuclei, although recent (terminated) starbursts are possible in the active galaxies. The stellar velocity fields show no signs of non-circular motions, while the 1-0S(1) H_2 kinematics exhibit significant deviations from simple circular rotation. In the active galaxies the H_2 kinematics reveal inflow and outflow superimposed on disk rotation. Steady-state circumnuclear inflow is seen in three AGN, and hydrodynamical models indicate it can be driven by a large scale bar. In three of the five AGN, molecular outflows are spatially resolved. The outflows are oriented such that they intersect, or have an edge close to, the disk - which may be the source of molecular gas in the outflow. The relatively low speeds imply the gas will fall back onto the disk; and with moderate outflow rates, they will have only a local impact on the host galaxy. H_2 was detected in two inactive galaxies. These exhibit chaotic circumnuclear dust morphologies and have molecular structures that are counter-rotating with respect to the main gas component, which could lead to gas inflow in the near future. In our sample, all four galaxies with chaotic dust morphology in the circumnuclear region exist in moderately dense groups with 10-15 members where accretion of stripped gas can easily occur.
    07/2014;
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    ABSTRACT: The \emph{Grism Lens-Amplified Survey from Space} (GLASS) is a Hubble Space Telescope (\HST) Large Program, which will obtain 140 orbits of grism spectroscopy of the core and infall regions of 10 galaxy clusters, selected to be among the very best cosmic telescopes. Extensive \HST\ imaging is available from many sources including the CLASH and Frontier Field programs. We introduce the survey by analyzing spectra of faint multiply-imaged galaxies and $z\gtrsim6$ galaxy candidates obtained from the first seven orbits targeting the core of the Frontier Field cluster MACS0717.5+3745. Using the G102 and G141 grisms to cover the wavelength range 0.8--1.7$\mu$m, we confirm 4 strongly lensed systems by detecting emission lines in each of the images. For the 9 $z\gtrsim6$ galaxy candidates clear from contamination, we do not detect any emission line down to a 1-$\sigma$ noise level of $\sim$5$\times$10$^{-18}$\cgs. Taking lensing magnification into account, our flux sensitivity reaches $\sim$0.2--5$\times$10$^{-18}$\cgs. These limits over an uninterrupted wavelength range rule out the possibility that the high-$z$ galaxy candidates are instead strong line emitters at lower redshift. These results show that by means of careful modeling of the background--- and with the assistance of lensing magnification---interesting flux limits can be reached for large numbers of objects, avoiding pre-selection and the wavelength restrictions inherent to ground-based multi-slit spectroscopy. These observations confirm the power of slitless \HST\ spectroscopy even in fields as crowded as a cluster core.
    Galaxy Astrophysics. 01/2014;
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    ABSTRACT: High-quality Keck/LRIS long-slit spectra for a sample of 97 Type 1 local active galaxies selected from the Sloan Digital Sky Survey (0.02 ≦ z ≦ 0.1; MBH ≦107 M⊙) are used to study the relations between black hole mass (MBH) and host-galaxy properties. Of these objects, eight were found to be lacking broad Hβ emission lines previously observed in SDSS spectra. Based on seeing and PSF profile, we can exclude the lack of broad lines in the Keck spectra as being due to a telescope pointing error, missing the central AGN. These AGNs are classified as type 1 or type 1.5 Seyferts according to the characteristic presence of broad lines in SDSS spectra, and as 1.8 or 1.9 Seyferts in Keck spectra. We discuss various explanations for this transition including time variation of the torus, time variation of the broad line region, and galaxy mergers resulting in an AGN off-center from the host-galaxy nucleus (including the possibility of a gravitational recoil). Follow up observations at Lick Observatory are used to constrain the different scenarios.
    01/2014;
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    ABSTRACT: We present near-infrared emission line counts and luminosity functions from the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields observed using both the G102 and G141 grism. Using these derived emission line counts we make predictions for future space missions, like WFIRST, that will make extensive use of slitless grism spectroscopy in the near-IR over large areas of sky. The WISP survey is sensitive to fainter flux levels (3-5x10^-17 ergs/s/cm2) than the near-infrared grism missions aimed at baryonic acoustic oscillation cosmology (1-4x10^-16 ergs/s/cm2), allowing us to both investigate the fainter emission lines the large area surveys will be missing and make count predictions for the deeper grism pointings that are likely to be done over smaller areas. Cumulative number counts of 0.7<z<1.5 galaxies reach 10,000 square degrees above an H-alpha flux of 2x10^{-16} ergs/s/cm2. Galaxies with low H-alpha/[OIII] ratios are very rare at the brighter fluxes that future near-infrared grism surveys will probe; our survey finds no galaxies with H-alpha/[OIII < 0.95 that have H-alpha flux greater than 3x10^-16 ergs/s/cm2. We find good agreement between our derived luminosity functions and those from narrow band H-alpha surveys, like those of HiZELS (Sobral et al. 2013) and New Halpha (Ly et. 2011). The evolution in both the H-alpha luminosity function from z=0.3-1.5 and the [OIII] luminosity function from z=0.7-2.3 is almost entirely in the L* parameter, which steadily increases with redshift over those ranges. We will also present simulations of future large area near-infrared grism spectroscopy, based on the observed distributions of emission line fluxes, galaxy sizes, redshifts, H-alpha/[OIII] ratios, and equivalent widths seen in the WISP survey.
    01/2014;
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    ABSTRACT: The scaling relations between black hole mass and galaxy global properties indicate a close connection between black hole growth and galaxy evolution. Based on the M-sigma relation of the most updated reverberation-mapped AGNs, we determine the virial factor for AGN black hole mass recipes, and applied it to a sample of 42 moderate-luminosity AGNs at 0.4 and 0.6. The sample has been observed with the HST (ACS, NICMOS, and WFC3) and the Keck telescope in order to measure bulge luminosity and stellar velocity dispersion of their host galaxies. By investigating cosmic evolution of the M-bulge luminosity and M-sigma relations over the last 6 Gyr, we find that black holes in the past lived in a smaller or lower luminosity bulges compared to the present-day black holes, as consistent with various previous works. The uncertainty of the single-epoch black hole mass is still a dominant hindrance in unveiling the nature of the black hole-galaxy connection, particularly at high redshift.
    01/2014;
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    ABSTRACT: Near-infrared reverberation measurements have proven to be a valuable tool for mapping the location of hot dust in active galactic nuclei (AGNs). Ground-based campaigns have shown that the K-band continuum varies in response to changes in the optical continuum, and measurements of the K-band lag time give the size scale of the hot dust emission region, which likely corresponds to the dust sublimation radius. Reverberation measurements at longer wavelengths can add valuable information on the dust temperature profile in AGNs and the structure of the putative dusty torus. We have conducted a space based monitoring campaign of the Seyfert 1 galaxy Zw 229-015 using optical data from the Kepler Space Telescope and infrared data (3.6 micron) from the Spitzer Space telescope. We have also augmented the optical data with multiple ground based observatories. We have detected infrared reverberation both on short and long timescales.
    01/2014;
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    ABSTRACT: The main aim of this work is the characterization of physical properties of galaxies detected in the far infrared (FIR) in the AKARI Deep Field-South (ADF-S) survey. Starting from a catalog of the 1 000 brightest ADF-S sources in the WIDE-S (90$\mu$m) AKARI band, we constructed a subsample of galaxies with spectral coverage from the ultraviolet to the far infrared. We then analyzed the multiwavelength properties of this 90$\mu$m selected sample of galaxies. For galaxies without known spectroscopic redshifts we computed photometric redshifts using the codes Photometric Analysis for Redshift Estimate (Le PHARE) and Code Investigating GALaxy Emission (CIGALE), tested these photometric redshifts using spectroscopic redshifts, and compared the performances of both codes. To test the reliability of parameters obtained by fitting spectral energy distributions, a mock cataloge was generated. We built a large multiwavelength catalog of more than 500 ADF-S galaxies. We successfully fitted Spectral Energy Distributions of 186 galaxies with $\rm{\chi^2_{min}<4}$, and analyzed the output parameters of the fits. We conclude that our sample consists mostly of nearby actively star-forming galaxies, and all our galaxies have a relatively high metallicity. We estimated photometric redshifts for 113 galaxies from the whole ADF-S sample. Comparing the performance of Le PHARE and CIGALE, we found that CIGALE gives more reliable redshift estimates for our galaxies, which implies that including the IR photometry allows for substantial improvement of photometric redshift estimation.
    12/2013;
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    ABSTRACT: Context. We present the revised near- to mid-infrared catalogue of the AKARI North Ecliptic Pole deep survey. The survey has the unique advantage of continuous filter coverage from 2 to 24 μm over nine photometric bands, but the initial version of the survey catalogue leaves room for improvement in the image analysis stage; the original images are strongly contaminated by the behaviour of the detector and the optical system. Aims: The purpose of this study is to devise new image analysis methods and to improve the detection limit and reliability of the source extraction. Methods: We removed the scattered light and stray light from the Earth limb, and corrected for artificial patterns in the images by creating appropriate templates. We also removed any artificial sources due to bright sources by using their properties or masked them out visually. In addition, for the mid-infrared source extraction, we created detection images by stacking all six bands. This reduced the sky noise and enabled us to detect fainter sources more reliably. For the near-infrared source catalogue, we considered only objects with counterparts from ground-based catalogues to avoid fake sources. For our ground-based catalogues, we used catalogues based on the CFHT/MegaCam z' band, CFHT/WIRCam Ks band and Subaru/Scam z' band. Objects with multiple counterparts were all listed in the catalogue with a merged flag for the AKARI flux. Results: The detection limits of all mid-infrared bands were improved by ~20%, and the total number of detected objects was increased by ~2000 compared with the previous version of the catalogue; it now has 9560 objects. The 5σ detection limits in our catalogue are 11, 9, 10, 30, 34, 57, 87, 93, and 256 μJy in the N2, N3, N4, S7, S9W, S11, L15, L18W, and L24 bands, respectively. The astrometric accuracies of these band detections are 0.48, 0.52, 0.55, 0.99, 0.95, 1.1, 1.2, 1.3, and 1.6 arcsec, respectively. The false-detection rate of all nine bands was decreased to less than 0.3%. In total, 27 770 objects are listed in the catalogue, 11 349 of which have mid-infrared fluxes. The catalogue is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/A132 or at the ISAS/JAXA observers page, http://www.ir.isas.jaxa.jp/ASTRO-F/Observation/
    Astronomy and Astrophysics 11/2013; · 5.08 Impact Factor
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    ABSTRACT: We present the results of the analysis of multiwavelength Spectral Energy Distributions (SEDs) of far-infrared galaxies detected in the AKARI Deep Field-South (ADF--S) Survey. The analysis uses a carefully selected sample of 186 sources detected at the 90 $\mu$m AKARI band, identified as galaxies with cross-identification in public catalogues. For sources without known spectroscopic redshifts, we estimate photometric redshifts after a test of two independent methods: one based on using mainly the optical -- mid infrared range, and one based on the whole range of ultraviolet -- far infrared data. We observe a vast improvement in the estimation of photometric redshifts when far infrared data are included, compared with an approach based mainly on the optical -- mid infrared range. We discuss the physical properties of our far-infrared-selected sample. We conclude that this sample consists mostly of rich in dust and young stars nearby galaxies, and, furthermore, that almost 25% of these sources are (Ultra)Luminous Infrared Galaxies. Average SEDs normalized at 90 $\mu$m for normal galaxies (138 sources), LIRGs (30 sources), and ULIRGs (18 galaxies) a the significant shift in the peak wavelength of the dust emission, and an increasing ratio between their bolometric and dust luminosities which varies from 0.39 to 0.73.
    Earth, Planets, and Space. 10/2013; 65(10).
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    ABSTRACT: The WFC3 Infrared Spectroscopic Parallel (WISP) Survey uses over 1300 HST orbits to study galaxy evolution over a majority of cosmic history. Its slitless grism spectroscopy over a wide, continuous spectral range (0.8-1.7 micron) provides an unbiased selection of thousands of emission line galaxies over 0.5 < z < 2.5. Hundreds of these galaxies are detected in multiple emission lines, allowing for important diagnostics of metallicity and dust extinction. We propose deep 3.6 micron imaging (5 sigma, 0.9 micro-Jy) of 40 of the deepest WISP fields observed with the combination of G102+G141 grisms, in order to detect emission-line galaxies down to 0.1 L*. Combined with our HST optical and near-IR photometry, these IRAC data will be critical to determining accurate stellar masses for both passive and active galaxies in our survey. We will determine the evolution of the faint end slope of the stellar mass function and the mass-metallicity relation down to low-mass galaxies, including measurement of a possible mass-metallicity-SFR fundamental plane. The addition of the IRAC photometry will also provide much stronger constraints on dust extinction and star formation history, especially when combined with information available from the emission lines themselves.
    Spitzer Proposal. 10/2013;
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    ABSTRACT: We propose to image 6 deg^2 in the North Ecliptic Pole (NEP) with IRAC to determine the origin of Extragalactic Background Light (EBL) fluctuations. These Spitzer images will be combined with CIBER data at 1.1 and 1.6 um, and Akari data at 2.4, 3.2, and 4.1 um, to probe the spectrum and band-to-band correlations of the fluctuations. The fluctuations have been reported by Spitzer and Akari, and are now positively detected in new and CIBER data, but their origin is controversial. This multi-wavelength analysis will allow us to determine if EBL fluctuations arise from epoch of reionization galaxies or diffuse intra-halo light emission both by measuring their spectral energy distribution (SED) from 1.0 to 4.5 um, and by measuring the cross-correlation between different bands. The analysis uses multiple field combinations in Spitzer, CIBER and Akari data to carry out a robust measurement with multiple data combinations for internal consistency tests. In addition, the proposed survey will be used in conjunction with Akari and Herschel data in the NEP survey that has the most comprehensive multi-band infrared coverage of any degree-scale field on the sky and the best available constraints on dust phases (e.g. PAH, silicate absorption, AGN dust tori, GMCs) in galaxies. We will use this multi-wavelength coverage to cross-identify IRAC counterparts to Herschel and Akari sources and obtain SEDs of dusty, star bursting galaxies at z ~ 1 to 3 from the UV to radio, and obtain accurate PAH luminosities of Akari 7.7 um-rest detected galaxies and AGNs.
    Spitzer Proposal. 10/2013;
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    ABSTRACT: The main energy-generating mechanisms in galaxies are black hole (BH) accretion and star formation (SF) and the interplay of these processes is driving the evolution of galaxies. MIR/FIR spectroscopy are able to distinguish between BH accretion and SF, as it was shown in the past by infrared spectroscopy from the space by the Infrared Space Observatory and Spitzer. Spitzer and Herschel spectroscopy together can trace the AGN and the SF components in galaxies, with extinction free lines, almost only in the local Universe, except for a few distant objects. One of the major goals of the study of galaxy evolution is to understand the history of the luminosity source of galaxies along cosmic time. This goal can be achieved with far-IR spectroscopic cosmological surveys. SPICA in combination with ground based large single dish submillimeter telescopes, such as CCAT, will offer a unique opportunity to do this. We use galaxy evolution models linked to the observed MIR-FIR counts (including Herschel) to predict the number of sources and their IR lines fluxes, as derived from observations of local galaxies. A shallow survey in an area of 0.5 square degrees, with a typical integration time of 1 hour per pointing, will be able to detect thousands of galaxies in at least three emission lines, using SAFARI, the far-IR spectrometer onboard of SPICA.
    09/2013;
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    ABSTRACT: Several lines of argument support the existence of a link between activity at the nuclei of galaxies, in the form of an accreting supermassive black hole, and star-formation activity in these galaxies. The exact nature of this link is still under debate. Radio jets have long been argued to be an ideal mechanism that allows AGN to interact with their host galaxy and regulate star-formation. In this context, we are using a sample of radio sources in the North Ecliptic Pole (NEP) field to study the nature of the putative link between AGN activity and star-formation. This is done by means of spectral energy distribution (SED) fitting. We use the excellent spectral coverage of the AKARI infrared space telescope together with the rich ancillary data available in the NEP to build SEDs extending from UV to far-IR wavelengths. Through SED fitting we constrain both the AGN and host galaxy components. We find a significant AGN component in our sample of relatively faint radio-sources ($<$mJy), that increases in power with increasing radio-luminosity. At the highest radio-luminosities, the presence of powerful jets dominates the radio emission of these sources. A positive correlation is found between the luminosity of the AGN component and that of star-formation in the host galaxy, independent of the radio luminosity. By contrast, for a given redshift and AGN luminosity, we find that increasing radio-luminosity leads to a decrease in the specific star-formation rate. The most radio-loud AGN are found to lie on the main sequence of star-formation for their respective redshifts. For the first time, such a two-sided feedback process is seen in the same sample. We conclude that radio jets do suppress star-formation in their host galaxies but appear not to totally quench it. Our results therefore support the maintenance nature of "radio-mode" feedback from radio-AGN jets.
    09/2013; 784(2).
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    ABSTRACT: We combine Hubble Space Telescope (HST) G102 & G141 NIR grism spectroscopy with HST/WFC3-UVIS, HST/WFC3-IR and Spitzer/IRAC[3.6\mu m] photometry to assemble a sample of massive (log(M_star/M_sun) ~ 11) and quenched galaxies at z~1.5. Our sample of 41 galaxies is the largest with G102+G141 NIR spectroscopy for quenched sources at these redshifts. In contrast to the local Universe, z~1.5 quenched galaxies in the high-mass range have a wide range of stellar population properties. We find their SEDs are well fitted with exponentially decreasing SFHs, and short star-formation time-scales (\tau<100Myr). Quenched galaxies also show a wide distribution in ages, between 1-4Gyr. In the (u-r)_0-versus-mass space quenched galaxies have a large spread in rest-frame color at a given mass. Most quenched galaxies populate the z~1.5 red-sequence (RS), but an important fraction of them (32%) have substantially bluer colors. Although with a large spread, we find that the quenched galaxies ON the RS have older median ages (3.1Gyr) than the quenched galaxies OFF the RS (1.5Gyr). We also show that a rejuvenated SED cannot reproduce the observed stacked spectra of (the bluer) quenched galaxies OFF the RS. We derive the upper limit on the fraction of massive galaxies ON the RS at z~1.5 to be <43%. We speculate that the young quenched galaxies OFF the RS are in a transition phase between vigorous star formation at z>2 and the z~1.5 RS. According to their estimated ages, the time required for quenched galaxies OFF the RS to join their counterparts ON the z~1.5 RS is of the order of ~1Gyr.
    The Astrophysical Journal 09/2013; 778(2). · 6.73 Impact Factor
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    ABSTRACT: We present near-infrared emission line counts and luminosity functions from the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields (0.037 deg^2) observed using both the G102 and G141 grisms. Altogether we identify 1048 emission line galaxies with observed equivalent widths greater than 40 Angstroms, 467 of which have multiple detected emission lines. The WISP survey is sensitive to fainter flux levels (3-5x10^-17 ergs/s/cm^2) than the future space near-infrared grism missions aimed at baryonic acoustic oscillation cosmology (1-4x10^-16 ergs/s/cm^2), allowing us to probe the fainter emission line galaxies that the shallower future surveys may miss. Cumulative number counts of 0.7<z<1.5 galaxies reach 10,000 deg^-2 above an H-alpha flux of 2x10^-16 ergs/s/cm^2. H-alpha-emitting galaxies with comparable [OIII] flux are roughly 5 times less common than galaxies with just H-alpha emission at those flux levels. Galaxies with low H-alpha/[OIII] ratios are very rare at the brighter fluxes that future near-infrared grism surveys will probe; our survey finds no galaxies with H-alpha/[OIII] < 0.95 that have H-alpha flux greater than 3x10^-16 ergs/s/cm^2. Our H-alpha luminosity function contains a comparable number density of faint line emitters to that found by the NICMOS near-infrared grism surveys, but significantly fewer (factors of 3-4 less) high luminosity emitters. We also find that our high redshift (z=0.9-1.5) counts are in agreement with the high redshift (z=1.47) narrow band H-alpha survey of HiZELS (Sobral et al. 2013), while our lower redshift luminosity function (z=0.3-0.9) falls slightly below their z=0.84 result. The evolution in both the H-alpha luminosity function from z=0.3--1.5 and the [OIII] luminosity function from z=0.7-2.3 is almost entirely in the L* parameter, which steadily increases with redshift over those ranges.
    The Astrophysical Journal 05/2013; · 6.73 Impact Factor
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    ABSTRACT: We present results of an on-going program to measure AGN feedback in Seyfert galaxies using integral-field spectroscopy and adaptive optics at Keck Observatory and VLT. Our integral-field observations are revealing AGN-driven outflows of ionized gas in Seyfert galaxies. By resolving the inner 10-40 parsecs, we are successfully modeling them as biconical structures, in which the ionized gas first accelerates and then decelerates. The model parameters provide crucial information on the orientation, geometry and kinematics of the outflows, which is used to estimate mechanical feedback from the AGN: mass and kinetic energy transferred to the interstellar medium. Mass outflow rates can be 102-104 times greater than accretion rates, but in some cases, they are comparable to the estimated inflow rates to the central 10-25 pc, suggesting that the outflows may remove a considerable amount of the infalling gas before it reaches the accretion disk. In half of the AGN measured so far, the kinetic energy of the outflows appears sufficient to provide the eagerly-sought AGN feedback invoked to explain fundamental galaxy properties such as the M BH - σ* relation (0.5-5 L bol). The other AGN, which lack powerful outflows, also have weaker and more compact radio jets.
    Proceedings of the International Astronomical Union 03/2013; 8(S292):363-366.
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    ABSTRACT: We present the first Kepler monitoring of a strongly variable BL Lac, W2R1926+42. The light curve covers 181 days with ~0.2% errors, 30 minute sampling and >90% duty cycle, showing numerous delta I/I > 25% flares over timescales as short as a day. The flux distribution is highly skewed and non-Gaussian. The variability shows a strong rms-flux correlation with the clearest evidence to date for non-linearity in this relation. We introduce a method to measure periodograms from the discrete autocorrelation function, an approach that may be well-suited to a wide range of Kepler data. The periodogram is not consistent with a simple power-law, but shows a flattening at frequencies below 7x10-5 Hz. Simple models of the power spectrum, such as a broken power law, do not produce acceptable fits, indicating that the Kepler blazar light curve requires more sophisticated mathematical and physical descriptions than currently in use.
    The Astrophysical Journal 02/2013; 766(1). · 6.73 Impact Factor
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    ABSTRACT: Spectroscopic observations of Hα and Hβ emission lines of 128 star-forming galaxies in the redshift range 0.75 z 1.5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (Hα/Hβ). We present dust extinction as a function of Hα luminosity (down to 3 × 10 41 erg s −1), galaxy stellar mass (reaching 4 × 10 8 M), and rest-frame Hα equivalent width. The faintest galaxies are two times fainter in Hα luminosity than galaxies previously studied at z ∼ 1.5. An evolution is observed where galaxies of the same Hα luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower Hα luminosity galaxies in our sample are found to be consistent with no dust extinction. We find an anti-correlation of the [O iii] λ5007/Hα flux ratio as a function of luminosity where galaxies with L Hα < 5 × 10 41 erg s −1 are brighter in [O iii] λ5007 than Hα. This trend is evident even after extinction correction, suggesting that the increased [O iii] λ5007/Hα ratio in low-luminosity galaxies is likely due to lower metallicity and/or higher ionization parameters.
    The Astrophysical Journal 02/2013; 763:145. · 6.73 Impact Factor
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    ABSTRACT: We present rest-frame optical spectroscopy for ~200 low-mass galaxies at z ≤ 0.7. Our sample of emission-line galaxies were selected by their excess in narrowband filters from the Subaru Deep Field. We construct the Baldwin-Phillips-Terlevich (BPT) and Mass-Excitation (MEx; Juneau et al.) diagrams, simultaneously determine gas-phase metallicity and the ionization parameter from available emission lines, and determine the electron density from Sulfur emission lines where available. We find that the majority of our galaxies are photo-ionized by stars. Their emission-line flux ratios occupy the upper left end of the BPT and MEx diagnostic diagrams. This is in stark comparison to the local SDSS sample, and suggests a higher ionization state in low-mass galaxies. Our measurements of the [OIII] λ5007/[OII] λ3727 flux ratio are also consistent with this statement where we find ionization parameter of log(U) = -2.4 ± 0.3. We also estimate the electron density from the [SII] λλ6717,6732 emission-line ratio for a dozen of our galaxies, and find a median electron density of 900 cm-3. These measurements on the physical properties of the interstellar medium for emission-line galaxies are all similar to those seen in high-redshift galaxies, suggesting that our low-mass galaxies may in fact be low-redshift analogs to the high-redshift population.
    01/2013;
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    ABSTRACT: The discovery of close correlations between supermassive black holes (BHs) and their host-galaxy properties has sparked a flood of observational studies pertaining both to the local Universe and cosmic history over the last decade. Nevertheless, a clear understanding of their origin still eludes us. Uncertainty remains as to the fundamental driver of these relations, whether purely local and baryonic or global and dark matter dominated. While studying the evolution of these relations with cosmic time provides valuable clues, a definitive resolution of this conundrum relies on understanding the slope and scatter of local relations for AGNs. We discuss first results from a unique three-fold approach. (i) From a sample of ~100 Active Galactic Nuclei (AGNs) in the local Universe, we are in the process of building a robust baseline of the BH mass scaling relations (MBH-sigma, MBH-L, MBH-M), combining spatially-resolved Keck spectroscopy with SDSS imaging. (ii) We study the evolution of the MBH-sigma and MBH-L relations out to a look-back time of 4-6 Gyrs using Keck spectra and HST images. (iii) We are currently extending this study out to the pivotal cosmic time between the peak of AGN activity and the establishment of the present-day Hubble sequence, a look-back time of 8-10 Gyrs. We measure spheroid stellar masses using deep multi-color HST images from GOODS and determine the MBH-M relation. The results from our pilot studies (i) indicate that AGNs follow the same scaling relations as inactive galaxies. From (ii-iii) we conclude that BH growth precedes bulge assembly. Combining results from (i-iii) allows us to test the hypothesis that evolution is driven by disks being transformed into bulges.
    01/2013;

Publication Stats

4k Citations
725.08 Total Impact Points

Institutions

  • 2013
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tōkyō, Japan
  • 1988–2013
    • University of California, Los Angeles
      • • Department of Physics and Astronomy
      • • Division of Astronomy & Astrophysics
      Los Angeles, California, United States
  • 2012
    • Carnegie Institution for Science
      Washington, West Virginia, United States
    • Seoul National University
      • Department of Physics and Astronomy
      Seoul, Seoul, South Korea
  • 2011
    • University of Southern California
      Los Angeles, California, United States
  • 2005
    • National Astronomical Observatory of Japan
      • Division of Optical and Infrared Astronomy
      Edo, Tōkyō, Japan
  • 1994–2004
    • Tel Aviv University
      • Department of Physics and Astronomy
      Tell Afif, Tel Aviv, Israel
  • 1995–1999
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
    • CSU Mentor
      Long Beach, California, United States
  • 1996
    • University of Birmingham
      • School of Physics and Astronomy
      Birmingham, England, United Kingdom
  • 1990
    • NASA
      Washington, West Virginia, United States
  • 1989
    • Haverford College
      Norristown, Pennsylvania, United States
  • 1982
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, California, United States