Andrea M. Gilbert

SINFONI in the galactic center: young stars and infrared flares in the central light-month

We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the central 30 light days of the Galactic Center [...]. To a limiting magnitude of K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7 arcsec from the central black hole have spectral properties of B0-B9, main sequence stars. [...] all brighter early type stars have normal rotation velocities, similar to solar neighborhood stars. We [...] derive improved 3d stellar orbits for six of these S-stars in the central 0.5 arcsec. Their orientations in space appear random. Their orbital planes are not co-aligned with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We can thus exclude [...] that the S-stars as a group inhabit the inner regions of these disks. They also cannot have been located/formed in these disks [...]. [...] we conclude that the S-stars were most likely brought into the central light month by strong individual scattering events. The updated estimate of distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32 kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum spectral energy distributions of these flares are fit by a featureless, red power law [...]. The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from [...] radiative inefficient accretion flow in the central R~10 Rs region.

Extreme gas kinematics in the z=2.2 powerful radio galaxy MRC 1138-262: Evidence for efficient active galactic nucleus feedback in the early universe?

To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such feedback in the optical emission line gas around the z = 2.16 powerful radio galaxy MRC 1138-262, likely a massive galaxy in formation. The kiloparsec-scale kinematics, with FWHMs and relative velocities 2400 km s-1 and nearly spherical spatial distribution, do not resemble large-scale gravitational motion or starburst-driven winds. Order-of-magnitude timescale and energy arguments favor the AGN as the only plausible candidate to accelerate the gas, with a total energy injection of a few ?1060 ergs or more, necessary to power the outflow, and relatively efficient coupling between radio jet and ISM. Observed outflow properties are in gross agreement with the models and suggest that AGN winds might have a cosmological significance that is similar to, or perhaps larger than, starburst-driven winds if MRC 1138-262 is indeed archetypal. Moreover, the outflow has the potential to remove significant gas fractions (50%) from a >L* galaxy within a few tens to 100?Myr, fast enough to preserve the observed [?/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC 1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such a feedback in the optical emission line gas around the z=2.16 powerful radio galaxy MRC1138-262, likely a massive galaxy in formation. The kpc-scale kinematics, with FWHMs and relative velocities L* galaxy within a few 10 to 100 Myrs, fast enough to preserve the observed [alpha/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.

Kinematic Masses of Super-Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy*

Using high-resolution (R ~ 22,000) near-infrared (1.51-1.75 ?m) spectra from Keck Observatory, we measure the kinematic masses of two super-star clusters in M82. Cross-correlation of the spectra with template spectra of cool evolved stars gives stellar velocity dispersions of ?r = 15.9 ? 0.8 km s-1 for J0955505+694045 (MGG-9) and ?r = 11.4 ? 0.8 km s-1 for J0955502+694045 (MGG-11). The cluster spectra are dominated by the light of red supergiants and correlate most closely with template supergiants of spectral types M0 and M4.5. King model fits to the observed profiles of the clusters in archival Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectometer images give half-light radii of rhp = 2.6 ? 0.4 pc for MGG-9 and rhp = 1.2 ? 0.17 pc for MGG-11. Applying the virial theorem, we determine masses of 1.5 ? 0.3 ? 106 M? for MGG-9 and 3.5 ? 0.7 ? 105 M? for MGG-11 (where the quoted errors include ?r, rhp, and the distance). Population synthesis modeling suggests that MGG-9 is consistent with a standard initial mass function (IMF), whereas MGG-11 appears to be deficient in low-mass stars relative to a standard IMF. There is, however, evidence of mass segregation in the clusters, in which case the virial mass estimates would represent lower limits.

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A 13 Year Study of Spectral Variability in NGC 5548

We present the final installment of an intensive 13 year study of variations of the optical continuum and broad Hemission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 Hmeasurements. The Hvariations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r / L 1=2 ion . Moreover, the apparently linear nature of the correlation between the Hresponse time and the nonstellar optical continuum Fopt arises as a consequence of the changing shape of the continuum as it varies, specifically Fopt / F 0:56 UV . Subject headings: galaxies: active — galaxies: individual (NGC 5548) — galaxies: nuclei — galaxies: Seyfert

The Rest-Frame Optical Spectrum of MS 1512–cB58*

Moderate-resolution, near-IR spectroscopy of MS 1512-cB58 is presented, obtained during commissioning of the near-infrared spectrometer (NIRSPEC) on the Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground cluster MS 1512+36 makes it the best candidate for detailed study of the rest-frame optical properties of Lyman-break galaxies. In 80 minutes of on-source integration, we have detected Halpha, [N ii] lambdalambda6583, 6548, [O i] lambda6300, He i lambda5876, [O iii] lambdalambda5007, 4959, Hbeta, Hgamma, [O ii] lambda3727, and a strong continuum signal in the range of 1.29-2.46 µm. A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in contrast to the z=2.7233 calculated from UV observations of interstellar absorption lines. Using the Balmer line ratios, we find an extinction of E(B-V) = 0.27. Using the line strengths, we infer a star formation rate (SFR) of 620+/-18 M middle dot in circle yr-1 (H0=75, q0=0.1, and Lambda=0), which is a factor of 2 higher than that measured from narrowband imaging observations of the galaxy but is a factor of almost 4 lower than the SFR inferred from the UV continuum luminosity. The width of the Balmer lines yields a mass of Mvir=1.2x1010 M middle dot in circle. We find that the oxygen abundance is 13 solar, in good agreement with other estimates of the metallicity. However, we infer a high nitrogen abundance, which may argue for the presence of an older stellar population.

A Survey of Organic Volatile Species in Comet C/1999 H1 (Lee) Using NIRSPEC at the Keck Observatory

The organic volatile composition of the long-period comet C/1999 H1 (Lee) was investigated using the —rst of a new generation of cross-dispersed cryogenic infrared spectrometers (NIRSPEC, at the Keck Observatory atop Mauna Kea, HI). On 1999 August 19¨21 the organics spectral region (2.9¨3.7 km) was completely sampled at both moderate and high dispersion, along with the CO fundamental region (near 4.67 km), revealing emission from water, carbon monoxide, methanol, methane, ethane, acetylene, and hydrogen cyanide. Many new multiplets from OH in the 1¨0 band were seen in prompt emission, and numerous new spectral lines were detected. Several spectral extracts are shown, and global production rates are presented for seven parent volatiles. Carbon monoxide is strongly depleted in comet Lee relative to comets Hyakutake and Hale-Bopp, demonstrating that chemical diversity occurred in the giant

Rejection of the Binary Broad-Line Region Interpretation of Double-peaked Emission Lines in Three Active Galactic Nuclei

It has been suggested that the peculiar double-peaked Balmer lines of certain broad-line radio galaxies come from individual broad-line regions associated with the black holes of a supermassive binary. We continue to search for evidence of the radial velocity variations characteristics of a double-lined spectroscopic binary that are required in such a model. After spectroscopic monitoring of three suitable candidates (Arp 102B, 3C 390.3, and 3C 332) spanning two decades, we find no such long-term systematic changes in radial velocity. A trend noticed by Gaskell in one of the Balmer-line peaks of 3C 390.3 before 1988 did not continue after that year, invalidating his inferred orbital period and mass. Instead, we find lower limits on the plausible orbital periods that would require the assumed supermassive binaries in all three objects to have total masses in excess of 1010 M☉. In the case of 3C 390.3, the total binary mass must exceed 1011 M☉ to satisfy additional observational constraints on the inclination angle. We argue that such large binary black hole masses are difficult to reconcile with other observations and with theory. In addition, there are peculiar properties of the line profiles and flux ratios in these objects that are not explained by ordinary broad-line region cloud models. We therefore doubt that the double-peaked line profiles of Arp 102B, 3C 390.3, and 3C 332 arise in pairs of broad-line regions. Rather, they are much more likely to be intimately associated with single black holes. The recent discoveries of transient but otherwise similar double-peaked emission lines in nearby active galactic nuclei bolster the view that double-peaked emission lines are commonly produced by a single compact source.

Feedback in the Antennae Galaxies (NGC 4038/9). I. High-Resolution Infrared Spectroscopy of Winds from Super Star Clusters* **

We present high-resolution (R {approx} 24,600) near-IR spectroscopy of the youngest super star clusters (SSCs) in the prototypical starburst merger, the Antennae Galaxies. These SSCs are young (3-7 Myr old) and massive (10{sup 5}-10{sup 7} M{sub {circle_dot}} for a Kroupa IMF) and their spectra are characterized by broad, extended Brackett {gamma} emission, so we refer to them as emission-line clusters (ELCs) to distinguish them from older SSCs. The Br {gamma} lines of most ELCs have supersonic widths (60-110 km s{sup -1} FWHM) and non-Gaussian wings whose velocities exceed the clusters escape velocities. This high-velocity unbound gas is flowing out in winds that are powered by the clusters massive O and W-R stars over the course of at least several crossing times. The large sizes of some ELCs relative to those of older SSCs may be due to expansion caused by these outflows; many of the ELCs may not survive as bound stellar systems, but rather dissipate rapidly into the field population. The observed tendency of older ELCs to be more compact than young ones is consistent with the preferential survival of the most concentrated clusters at a given age.

Measurement of [O III] emission in Lyman-break galaxies

Measurements of [O III] emission in Lyman-break galaxies (LBGs) at z > 3 are presented. Four galaxies were observed with narrowband filters using the near-IR camera on the Keck I 10 m telescope. A fifth galaxy was observed spectroscopically during the commissioning of NIRSPEC, the new infrared spectrometer on Keck II. The emission-line spectrum is used to place limits on the metallicity. Comparing these new measurements with others available from the literature, we find that strong oxygen emission in LBGs may suggest subsolar metallicity for these objects. The [O III] λ5007 line is also used to estimate the star formation rate (SFR) of the LBGs. The inferred SFRs are higher than those estimated from the UV continuum, and may be evidence for dust extinction.

High-Precision Stellar Radial Velocities in the Galactic Center*

We present radial velocities for 85 cool stars projected onto the central parsec of the Galaxy. The majority of these velocities have relative errors of ~1 km s-1, or a factor of ~30-100 smaller than those previously obtained with proper-motion or other radial velocity measurements for a similar stellar sample. The error in a typical individual stellar velocity, including all sources of uncertainty, is 1.7 km s-1. Two similar data sets were obtained 1 month apart, and the total error in the relative velocities is 0.80 km s-1 in the case where an object is common to both data sets. The data are used to characterize the velocity distribution of the old population in the Galactic center. We find that the stars have a Gaussian velocity distribution with a mean heliocentric velocity of -10.1 ± 11.0 km s-1 (blueshifted) and a standard deviation of 100.9 ± 7.7 km s-1; the mean velocity of the sample is consistent with no bulk line-of-sight motion with respect to the local standard of rest. At the 1 σ level, the data are consistent with a symmetric velocity distribution about any arbitrary axis in the plane of the sky. We find evidence for a flattening in the distribution of late-type stars within a radius of ~0.4 pc and infer a volume density distribution of r-1/4 in this region. Finally, we establish a first epoch of radial velocity measurements that can be compared with subsequent epochs to measure small accelerations (1 km s-1 yr-1), corresponding to the magnitude expected over a time span of several years for stars nearest to Sgr A*.