Amiel Sternberg

Max Planck Institute for Extraterrestrial Physics, Arching, Bavaria, Germany

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Publications (37)225.69 Total impact

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    Natalie Mashian, Amiel Sternberg, Abraham Loeb
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    ABSTRACT: Walter et al. (20012) have recently identified the J=6-5, 5-4, and 2-1 CO rotational emission lines, and [C_{II}] fine-structure emission line from the star-forming interstellar medium in the high-redshift submillimeter source HDF 850.1, at z = 5.183. We employ large velocity gradient (LVG) modeling to analyze the spectra of this source assuming the [C_{II}] and CO emissions originate from (i) separate unvirialized regions, (ii) separate virialized regions, (iii) uniformly mixed unvirialized region, and (iv) uniformly mixed virialized regions. We present the best fit set of parameters, including for each case the ratio $\alpha$ between the total hydrogen/helium gas mass and the CO(1-0) line luminosity. We also present computations of the ratio of H_{2} mass to [C_{II}] line-luminosity for optically thin conditions, for a range of gas temperatures and densities, for direct conversion of [C_{II}] line-luminosities to "dark-H_{2}" masses. For HDF 850.1 we find that a model in which the CO and C^{+} are uniformly mixed in gas that is shielded from UV radiation, requires a cosmic-ray or X-ray ionization rate of $\zeta \approx$ 10^{-13} s^{-1}, plausibly consistent with the large star-formation rate ($\sim$ 10^{3} M$_{\odot}$ yr^{-1}) observed in this source. Enforcing the cosmological constraint posed by the abundance of dark matter halos in the standard $\Lambda$CDM cosmology and taking into account other possible contributions to the total gas mass, we find that three of these four models are less likely at the 2$\sigma$ level. We conclude that modeling HDF 850.1's ISM as a collection of unvirialized molecular clouds with distinct CO and C^{+} layers, for which $\alpha$ = 0.6 M$_{\odot}$ (K km s^{-1} pc^{2})^{-1} for the CO to H_{2} mass-to-luminosity ratio, (similar to the standard ULIRG value), is most consistent with the $\Lambda$CDM cosmology.
    Monthly Notices of the Royal Astronomical Society 02/2013; 435(3). · 5.52 Impact Factor
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    ABSTRACT: We analyze the spectra, spatial distributions and kinematics of Ha, [NII] and [SII] emission in a sample of 42, z~2.2 UV/optically selected star forming galaxies (SFGs) from the SINS & zC-SINF surveys, 35 of which were observed in the adaptive optics mode of SINFONI. This is supplemented by kinematic data from 48 z~1-2.5 galaxies from the literature. We find that the kinematic classification of the high-z SFGs as `dispersion dominated' or `rotation dominated' correlates most strongly with their intrinsic sizes. Smaller galaxies are more likely `dispersion-dominated' for two main reasons: 1) The rotation velocity scales linearly with galaxy size but intrinsic velocity dispersion does not depend on size, and as such, their ratio is systematically lower for smaller galaxies, and 2) Beam smearing strongly decreases large-scale velocity gradients and increases observed dispersion much more for galaxies with sizes at or below the resolution. Dispersion dominated SFGs may thus have intrinsic properties similar to `rotation dominated' SFGs, but are primarily more compact, lower mass, less metal enriched and may have higher gas fractions, plausibly because they represent an earlier evolutionary state.
    The Astrophysical Journal 11/2012; 767(2). · 6.73 Impact Factor
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    ABSTRACT: Based on SINFONI Ha, [NII] and [SII] AO data of 30 z \sim 2 star-forming galaxies (SFGs) from the SINS and zcSINF surveys, we find a strong correlation of the Ha broad flux fraction with the star formation surface density of the galaxy, with an apparent threshold for strong outflows occurring at 1 Msun yr^-1 kpc^-2. Above this threshold, we find that SFGs with logm_\ast>10 have similar or perhaps greater wind mass loading factors (eta = Mdotout/SFR) and faster outflow velocities than lower mass SFGs. This trend suggests that the majority of outflowing gas at z \sim 2 may derive from high-mass SFGs, and that the z \sim 2 mass-metallicity relation is driven more by dilution of enriched gas in the galaxy gas reservoir than by the efficiency of outflows. The mass loading factor is also correlated with the SFR and inclination, such that more star-forming and face-on galaxies launch more powerful outflows. For galaxies that have evidence for strong outflows, we find that the broad emission is spatially extended to at least the half-light radius (\sim a few kpc). We propose that the observed threshold for strong outflows and the observed mass loading of these winds can be explained by a simple model wherein break-out of winds is governed by pressure balance in the disk. Using the ratio of the [SII] doublet in a broad and narrow component, we find that outflowing gas has a density of \sim10-100 cm^-3, significantly less than that of the star forming gas (600 cm^-3).
    The Astrophysical Journal 07/2012; 761(1). · 6.73 Impact Factor
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    ABSTRACT: We present the results of a Herschel-PACS study of a sample of 97 LINERs at redshift z\sim 0.3 selected from the zCOSMOS survey. Of these sources, 34 are detected in a least one PACS band, enabling reliable estimates of the far-infrared L(FIR) luminosities, and a comparison to the FIR luminosities of local LINERs. Many of our PACS-detected LINERs are also UV sources detected by Galex. Assuming that the FIR is produced in young dusty star-forming regions, the typical star-formation rates (SFRs) for the host galaxies in our sample is \sim 10 M_Sun yr-1, 1-2 orders of magnitude larger than in many local LINERs. Given stellar masses inferred from optical/NIR photometry of the (unobscured) evolved stellar populations, we find that the entire sample lies close to the star-forming "main sequence" for galaxies at redshift 0.3. For young star-forming regions, the H\alpha- and UV-based estimates of the SFRs are much smaller than the FIR-based estimates, by factors \sim 30, even assuming that all of the H\alpha\ emission is produced by O-star ionization rather than by the AGNs. These discrepancies may be due to large (and uncertain) extinctions towards the young stellar systems. Alternatively, the H\alpha\ and UV emissions could be tracing residual star-formation in an older less obscured population with decaying star formation. We also compare L(SF) and L(AGN) in local LINERs and in our sample and comment on the problematic use of several line diagnostic diagrams in cases similar to the sample under study.
    The Astrophysical Journal 01/2012; 753(2). · 6.73 Impact Factor
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    ABSTRACT: Many observed massive star-forming z 2 galaxies are large disks that exhibit irregular morphologies, with 1 kpc, 108-1010M clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M * 1010.5M galaxies in 1012M halos at z 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f g 50%), and high specific star formation rates (1 Gyr–1). In accord with recent models, giant clumps (M clump (5 × 108-109)M) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.
    The Astrophysical Journal 12/2011; 745(1):11. · 6.73 Impact Factor
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    ABSTRACT: The zCOSMOS SINFONI project is aimed at studying the physical and kinematical properties of a sample of massive z~1.4-2.5 star-forming galaxies, through SINFONI near-IR integral field spectroscopy (IFS), combined with the multi-wavelength information from the zCOSMOS (COSMOS) survey. The project is based on 1 hour of natural-seeing observations per target, and Adaptive Optics (AO) follow-up for a major part of the sample, which includes 30 galaxies selected from the zCOSMOS/VIMOS spectroscopic survey. This first paper presents the sample selection, and the global physical characterization of the target galaxies from multicolor photometry, i.e., star formation rate (SFR), stellar mass, age, etc. The Halpha integrated properties such as, flux, velocity dispersion, and size, are derived from the natural-seeing observations, while the follow up AO observations will be presented in the next paper of this series. Our sample appears to be well representative of star-forming galaxies at z~2, covering a wide range in mass and SFR. The Halpha integrated properties of the 25 Halpha detected galaxies are similar to those of other IFS samples at the same redshifts. Good agreement is found among the SFRs derived from Halpha luminosity and other diagnostic methods, provided the extinction affecting the Halpha luminosity is about twice that affecting the continuum. A preliminary kinematic analysis, based on the maximum observed velocity difference across the source, and on the integrated velocity dispersion, indicates that the sample splits nearly 50-50 into rotation-dominated and velocity dispersion-dominated galaxies, in good agreement with previous surveys.
    The Astrophysical Journal 09/2011; 743(1). · 6.73 Impact Factor
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    ABSTRACT: We study the growth of dark matter halos in the concordance LCDM cosmology using several N-body simulations of large cosmological volumes. We build merger trees from the Millennium and Millennium-II simulations, covering a range 10^9-10^15 Msun in halo mass and 1-10^5 in merger mass ratio. Our algorithm takes special care of halo fragmentation and ensures that the mass contribution of each merger to halo growth is only counted once. This way the integrated merger rate converges and we can consistently determine the contribution of mergers of different mass ratios to halo growth. We find that all resolved mergers, up to mass ratios of 10^5, contribute only ~60% of the total halo mass growth, while major mergers are subdominant, e.g. mergers with mass ratios smaller than 3:1 (10:1) contribute only ~20% (~30%). This is verified with an analysis of two additional simulation boxes, where we follow all particles individually throughout cosmic time. Our results are also robust against using several halo definitions. Under the assumption that the power-law behaviour of the merger rate at large mass ratios can be extrapolated to arbitrarily large mass ratios, it is found that, independently of halo mass, ~40% of the mass in halos comes from genuinely smooth accretion of dark matter that was never bound in smaller halos. We discuss possible implications of our findings for galaxy formation. One implication, assuming as is standard that the pristine intergalactic medium is heated and photoionized by UV photons, is that all halos accrete >40% of their baryons in smooth "cold" T>~10^4K gas, rather than as warm, enriched or clumpy gas or as stars. Comment: 11 pages, 9 figures. Accepted for publication in the Astrophysical Journal
    The Astrophysical Journal 05/2010; · 6.73 Impact Factor
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    ABSTRACT: We present new observations of the nuclear star cluster in the central parsec of the Galaxy with the adaptive optics assisted, integral field spectrograph SINFONI on the ESO/VLT. Our work allows the spectroscopic detection of early- and late-type stars to mK ≥ 16, more than 2 mag deeper than our previous data sets. Our observations result in a total sample of 177 bona fide early-type stars. We find that most of these Wolf Rayet (WR), O-, and B-stars reside in two strongly warped disks between 08 and 12'' from Sgr A*, as well as a central compact concentration (the S-star cluster) centered on Sgr A*. The later type B-stars (mK >15) in the radial interval between 08 and 12'' seem to be in a more isotropic distribution outside the disks. The observed dearth of late-type stars in the central few arcseconds is puzzling, even when allowing for stellar collisions. The stellar mass function of the disk stars is extremely top heavy with a best-fit power law of dN/dm m –0.45± 0.3. WR/O-stars were formed in situ in a single star formation event ~6 Myr ago, this mass function probably reflects the initial mass function (IMF). The mass functions of the S-stars inside 08 and of the early-type stars at distances beyond 12'' are compatible with a standard Salpeter/Kroupa IMF (best-fit power law of dN/dm m –2.15± 0.3).
    The Astrophysical Journal 12/2009; 708(1):834. · 6.73 Impact Factor
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    ABSTRACT: High signal-to-noise, representative spectra of star-forming galaxies at z ~ 2, obtained via stacking, reveal a high-velocity component underneath the narrow Hα and [N II] emission lines. When modeled as a single Gaussian, this broad component has FWHM 1500 km s–1; when modeled as broad wings on the Hα and [N II] features, it has FWHM 500 km s–1. This feature is preferentially found in the more massive and more rapidly star-forming systems, which also tend to be older and larger galaxies. We interpret this emission as evidence of either powerful starburst-driven galactic winds or active supermassive black holes (SMBHs). If galactic winds are responsible for the broad emission, the observed luminosity and velocity of this gas imply mass outflow rates comparable to the star formation rate. On the other hand, if the broad-line regions of active black holes account for the broad feature, the corresponding black holes masses are estimated to be an order of magnitude lower than those predicted by local scaling relations, suggesting a delayed assembly of SMBHs with respect to their host bulges.
    The Astrophysical Journal 07/2009; 701(2):955. · 6.73 Impact Factor
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    ABSTRACT: We present new near- and mid-infrared high angular resolution spectroscopic and imaging data of the nuclear region of NGC 7552. This galaxy is a face-on barred spiral galaxy with several circumnuclear rings. Our near-infrared images have subarcsecond resolution and reveal the spatial distribution of the J (1.25 μm), H (1.60 μm), K (2.20 μm) continuum and most of the prominent near-infrared K-band lines (Brγ, He I, H2 in emission and 12CO,13CO in absorption). Our N-band (10.5 μm) continuum image has an angular resolution of about 1'' and corresponds very well in structure with the JHK color maps and a published 6 cm radio continuum map. The data are combined with radio and far-infrared data available in the literature and interpreted in the framework of a starburst model. The result of the starburst model is used in connection with published near-infrared template star spectra to perform a spectral synthesis for the very nucleus as well as for selected regions in it. As a result we obtain a first insight into the different star formation histories of the nucleus and the 1 kpc circumnuclear ring. We also demonstrate that the star formation rate and efficiency are intimately associated with the dynamics of the stars and gas in the nucleus of NGC 7552. The combination of the starburst model with the spectral synthesis demonstrates for the first time the feasibility of this approach in the near-infrared. This approach validates the estimates of extinction and the contribution from hot dust made from JHK color diagrams and emission line ratios. It also proves in a consistent way that the emission from the ring originates in young stellar clusters. These clusters were formed in a decaying starburst about 107 yr ago with an upper mass cutoff well above 50 M☉. The K-band light from the nucleus most likely contains comparable contributions from an constant, old (≈ 1010 yr) and a decaying, young (≈ 107 yr) stellar population.
    The Astrophysical Journal 01/2009; 488(1):174. · 6.73 Impact Factor
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    ABSTRACT: We report the first direct observations of neutral, molecular gas streaming in the nucleus of NGC 1068 on scales of <30 pc using SINFONI near-infrared integral field spectroscopy. At a resolution of 0075, the flux map of 2.12 μm 1-0 S(1) molecular hydrogen emission around the nucleus in the central arcsec reveals two prominent linear structures leading to the active galactic nucleus from the north and south. The kinematics of the gas in these features are dominated by noncircular motions and indicate that material streams toward the nucleus on highly elliptical or parabolic trajectories, whose orientations are compatible with that of the disk plane of the galaxy. We interpret the data as evidence for fueling of gas to the central region. The radial transport rate from ~30 pc to a few parsecs from the nucleus is ~15 M ☉ yr–1. One of the infalling clouds lies directly in front of the central engine. We interpret it as a tidally disrupted streamer that forms the optically thick outer part of an amorphous clumpy molecular/dusty structure which contributes to the nuclear obscuration.
    The Astrophysical Journal 01/2009; 691(1):749. · 6.73 Impact Factor
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    ABSTRACT: The Infrared Space Observatory (ISO) Short-Wavelength Spectrometer (SWS) infrared spectroscopic observations of the nucleus of Seyfert galaxy NGC 4151, which are described in a companion paper, are used in conjunction with a compilation of UV to IR narrow emission line data to determine the spectral shape of the obscured extreme-UV continuum that photoionizes the narrow-line-emitting gas in the active galactic nucleus (AGN). We present a new method for determining the best-fitting photoionizing continuum and emission-line cloud model from a heterogeneous set of emission-line data. For NGC 4151, we find a best-fit model that reproduces the observed line fluxes to within a factor of 2 on average, and that is consistent with the observed geometry of the optical narrow-line region (NLR). Our model consists of a clumpy, optically thick (ionization-bounded) gas distribution, with a hydrogen gas density of ~1000 cm-3 and a volume-filling factor of 6.510-4. Our best-fitting spectral energy distribution (SED) falls sharply beyond the Lyman limit and then rises sharply again toward 100 eV. In particular, it does not display the "big blue bump" signature of a hot accretion disk. We find that this SED, which best reproduces the NLR line emission on the 100-500 pc scale, does not have enough UV photons to produce the observed broad-line region (BLR) recombination emission from the inner 1 pc. This suggests that the BLR is photoionized by the intrinsic continuum source, which does have a strong UV component (perhaps a big blue bump), but that this UV component is absorbed by material located between the NLR and BLR. Our analysis suggests that the absorber consists of ~51019 cm-2 of neutral hydrogen. Such an absorber has been independently detected by UV absorption lines. Using our new method, we confirm our previous conclusion that a big blue bump is present in the SED of the Seyfert 2 galaxy Circinus.
    The Astrophysical Journal 01/2009; 512(1):204. · 6.73 Impact Factor
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    Tal Alexander, Amiel Sternberg
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    ABSTRACT: We investigate microlensing amplification of faint stars in the dense stellar cluster in the Galactic center by the supermassive black hole, which is thought to coincide with the radio source Sgr A*. Such amplification events would appear very close to the position of Sgr A* and could be observed, in principle, during the monitoring of stellar proper motions in the Galactic center. We use observations of the near-infrared K-band (2.2 μm) luminosity function in the Galactic center and in Baade's window, as well as stellar population synthesis computations, to construct empirical and theoretical K luminosity function models for the inner 300 pc of the Galaxy. These, together with the observed dynamical properties of the central cluster and inner bulge, are used to compute the rates of microlensing events that amplify stars with different intrinsic luminosities above specified detection thresholds. We present computations of the lensing rates as functions of the event durations, which range from several weeks to a few years, for detection thresholds ranging from K0 = 16 to 19 mag. We find that events with durations shorter than a few months dominate the lensing rate because of the very high stellar densities and velocities very near the black hole, where the effective lens size is small. For the current detection limit of K0 = 17 mag, the total microlensing rate is 3 × 10-3 yr-1. The rate of events with durations ≥1 yr is 1 × 10-3 yr-1. The median value of the peak amplification for short events is ΔK ~ 0.75 mag above the detection threshold and is only weakly dependent on K0. Long events are rarer and are associated with more distant stars, stars at the low-velocity tail of the velocity distribution or stars that cross closer to the line of sight to Sgr A*. Therefore, the median peak amplifications of long events are larger and attain values ΔK ~ 1.5 mag above the threshold. Recent proper-motion studies of stars in the Galactic center have revealed the possible presence of one or two variable K-band sources very close to, or coincident with, the position of Sgr A*. These sources may have attained peak brightnesses of K ≈ 15 mag, about 1.5-2 mag above the observational detection limits, and appear to have varied on a timescale of ~1 yr. This behavior is consistent with long-duration microlensing amplification of faint stars by the central black hole. However, we estimate that the probability that a single such event could have been detected during the course of the recent proper-motion monitoring campaigns is ~0.5%. A 10-fold improvement in the detection limit and 10 yr of monthly monitoring could increase the total detection probability to ~20%.
    The Astrophysical Journal 01/2009; 520(1):137. · 6.73 Impact Factor
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    ABSTRACT: We present new Infrared Space Observatory Short Wavelength Spectrometer data for a sample of 27 starburst galaxies, and with these data we examine the issues of formation and evolution of the most massive stars in starburst galaxies. Using starburst models which incorporate time evolution, new stellar atmosphere models for massive stars, and a starburst model geometry derived from observations of the prototypical starburst M82, we model the integrated mid-infrared line ratio [Ne III](15.6 μm)/[Ne II](12.8 μm). This line ratio is sensitive to the hardness of the stellar energy distribution and therefore to the most massive stars present. We conclude from our models, with consideration of recent determinations of the stellar census in local, high-mass star-forming regions, that the [Ne III]/[Ne II] ratios we measure are consistent with the formation of massive (~50-100 M☉) stars in most starbursts. In this framework, the low nebular excitation inferred from the measured line ratios can be attributed to aging effects. By including estimates of the ratio of infrared-to-Lyman continuum luminosity for the galaxies in our sample, we further find that most starbursts are relatively short-lived (106-107 yr), only a few O star lifetimes. We discuss a possible cause of such short events: the effectiveness of stellar winds and supernovae in destroying the starburst environment.
    The Astrophysical Journal 12/2008; 539(2):641. · 6.73 Impact Factor
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    ABSTRACT: We present ~05 resolution near-infrared integral field spectroscopy of the Hα line emission of 14 z ~ 2 UV-selected BM/BX galaxies, obtained with SINFONI at the ESO Very Large Telescope. The average Hα half-light radius is r1/2 ≈ 4 h kpc, and line emission is detected over 20 h kpc in several sources. In nine galaxies, we detect spatially resolved velocity gradients, from 40 to 410 km s-1 over ~10 h kpc. The kinematics of the larger systems are generally consistent with orbital motions. Four galaxies are well described by rotating clumpy disks, and we extracted rotation curves out to radii 10 h kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities of vc ~ 180 ± 90 km s-1 and dynamical masses from ~0.5 to 25 × 1010 h M☉ within r1/2. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. Moreover, the specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average vc at 10 h kpc, the virial mass of the typical halo of a galaxy in our sample is 1011.7±0.5 h M☉. Kinematic modeling of the three best cases implies a ratio of vc to local velocity dispersion vc/σ ~ 2-4 and, accordingly, a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500 Myr. We also argue that if our BM/BX galaxies were initially gas-rich, their clumpy disks would subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr.
    The Astrophysical Journal 12/2008; 645(2):1062. · 6.73 Impact Factor
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    ABSTRACT: We report the definite spectroscopic identification of 40 OB supergiants, giants, and main-sequence stars in the central parsec of the Galaxy. Detection of their absorption lines has become possible with the high spatial and spectral resolution and sensitivity of the adaptive optics integral field spectrometer SPIFFI/SINFONI on the ESO VLT. Several of these OB stars appear to be helium- and nitrogen-rich. Almost all of the 80 massive stars now known in the central parsec (central arcsecond excluded) reside in one of two somewhat thick ( /R 0.14) rotating disks. These stellar disks have fairly sharp inner edges (R 1'') and surface density profiles that scale as R-2. We do not detect any OB stars outside the central 0.5 pc. The majority of the stars in the clockwise system appear to be on almost circular orbits, whereas most of those in the "counterclockwise" disk appear to be on eccentric orbits. Based on its stellar surface density distribution and dynamics, we propose that IRS 13E is an extremely dense cluster (ρcore 3 × 108 M pc-3) that has formed in the counterclockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of 6 ± 2 Myr. The K-band luminosity function of the massive stars suggests a top-heavy mass function and limits the total stellar mass contained in both disks to 1.5 × 104 M. Our data strongly favor in situ star formation from dense gas accretion disks for the two stellar disks. This conclusion is very clear for the clockwise disk and highly plausible for the counterclockwise system.
    The Astrophysical Journal 12/2008; 643(2):1011. · 6.73 Impact Factor
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    ABSTRACT: We report results from the first mid-infrared spectroscopic study of a comprehensive sample of 33 LINERs, observed with the Spitzer Space Telescope. We compare the properties of two different LINER populations: infrared-faint LINERs, with LINER emission arising mostly in compact nuclear regions, and infrared-luminous LINERs, which often show spatially extended (non-AGN) LINER emission. We show that these two populations can be easily distinguished by their mid-infrared spectra in three different ways: (1) their mid-IR spectral energy distributions (SEDs), (2) the emission features of polycyclic aromatic hydrocarbons (PAHs), and (3) various combinations of IR fine-structure line ratios. IR-luminous LINERs show mid-IR SEDs typical of starburst galaxies, while the mid-IR SEDs of IR-faint LINERs are much bluer. PAH flux ratios are significantly different in the two groups. Fine-structure emission lines from highly excited gas, such as [O IV], are detected in both populations, suggesting the presence of an additional AGN in a large fraction of IR-bright LINERs as well, which contributes little to the combined mid-IR light. The two LINER groups occupy different regions of mid-infrared emission-line excitation diagrams. The positions of the various LINER types in our diagnostic diagrams provide important clues regarding the power source of each LINER type. Most of these mid-infrared diagnostics can be applied at low spectral resolution, making AGN- and starburst-excited LINERs distinguishable at high redshifts as well.
    The Astrophysical Journal 12/2008; 653(1):L13. · 6.73 Impact Factor
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    ABSTRACT: Recent observations of UV/optically selected, massive star-forming galaxies at z ≈ 2 indicate that the baryonic mass assembly and star formation history is dominated by continuous rapid accretion of gas and internal secular evolution, rather than by major mergers. We use the Millennium Simulation to build new halo merger trees and extract halo merger fractions and mass accretion rates. We find that, even for halos not undergoing major mergers, the mass accretion rates are plausibly sufficient to account for the high star formation rates observed in z ≈ 2 disks. On the other hand, the fraction of major mergers in the Millennium Simulation is sufficient to account for the number counts of submillimeter galaxies (SMGs), in support of observational evidence that these are major mergers. When following the fate of these two populations in the Millennium Simulation to z = 0, we find that subsequent mergers are not frequent enough to convert all z ≈ 2 turbulent disks into elliptical galaxies at z = 0. Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at z ≈ 2 into observed massive cluster ellipticals at z = 0. We argue therefore, that secular and internal evolution must play an important role in the evolution of a significant fraction of z ≈ 2 UV/optically and submillimeter-selected galaxy populations.
    The Astrophysical Journal 12/2008; 688(2):789. · 6.73 Impact Factor
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    ABSTRACT: Spectroscopy in the mid-infrared spectral range provides a number of unique diagnostics of active galactic nuclei which can now be used thanks to ISO’s sensitivity and full wavelength coverage. Mid-infrared aromatic emission features are absent close to the AGN but can be strong on larger host galaxy scales, in particular if there is intense circumnuclear star formation. The rich.ne structure and coronal line spectrum can be used to reconstruct the otherwise unobservable extreme ultraviolet emission of the AGN. We find evidence for ‘bigblue bump’ emission from the accretion disk but also for neutral absorbers located inside the narrow line region. The ability of mid-infrared emission to penetrate dust allows to probe the structure of dusty narrow line regions, and to search for the obscured broad line region in Seyfert 2 galaxies.
    01/2008: pages 209-216;
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    ABSTRACT: The impact of active galactic nuclei on low-ionization nuclear emission-line regions (LINERs) remains a vigorous field of study. We present preliminary results from a study of the mid-infrared atomic emission lines of LINERs with the Spitzer Space Telescope. We assess the ubiquity and properties of AGN in LINERs using this data. We discuss what powers the mid-infrared emission lines and conclude that the answer depends unsurprisingly on the emission line ionization state and, more interestingly, on the infrared luminosity.
    09/2007;

Publication Stats

1k Citations
225.69 Total Impact Points

Institutions

  • 2008–2012
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 1997–2012
    • Tel Aviv University
      • Department of Physics and Astronomy
      Tell Afif, Tel Aviv, Israel
  • 2011
    • University of California, Santa Cruz
      Santa Cruz, California, United States
  • 2001
    • Carnegie Institution for Science
      Washington, West Virginia, United States