Lydia Moser

Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic Center

Context. There are a number of faint compact infrared excess sources in the central stellar cluster of the Milky Way. Their nature a nd origin is unclear. In addition to several isolated objects o f this kind there is a small but dense cluster of comoving sources (IRS13N) located∼3” west of SgrA* just 0.5” north of the bright IRS13E cluster of Wolf-Rayet and O-type stars. Based on the analysis of their color and brightness, there are two main possibilities: (1) they may be dust-embedded stars older than a few Myr, or (2) very young, dusty stars with ages younger than 1 Myr. Aims. We present a first K s-band identification and proper motions of the IRS13N member s, the high-velocity dusty S-cluster object (DSO, also referred to as G2), and other infrared excess sour ces in the central field. Goal is to constrain the nature of the se source. Methods. The L ′ - (3.8� m) Ks- (2.2� m) and H-band (1.65� m) observations were carried out using the NACO adaptive optics system at the ESO VLT. Proper motions were obtained by linear fitting of the stellar positions extracted by StarFinder as a functi on of time, weighted by positional uncertainties, and by Gaussian fitti ng from high-pass filtered and deconvolved images. We also pr esent results of near-infrared (NIR) H- and Ks-band ESO-SINFONI integral field spectroscopy of the Galact ic Center cluster ISR13N. Results. We show that within the uncertainties, the positions and proper motions of the IRS13N sources in Ks- and L ′ -band are identical. The HK−sL’ colors then indicate that the bright L ′ -band IRS13N sources are indeed dust-enshrouded stars rather than core-less dust clouds. The proper motions also show that the IRS13N sources are not strongly gravitationally bound to each other. Combined with their NIR colors, this implies that they have been formed recently. For the DSO we obtain proper motions and a Ks-L ′ -color. Conclusions. Most of the compact L ′ -band excess emission sources have a compact H- or Ks-band counterpart and therefore are likely stars with dust shells or disks. Our new results and or bital analysis from our previous work favor the hypothesis t hat the infrared excess IRS13N members and other dusty sources close to SgrA* are young dusty stars and that star formation at the Galactic Center (GC) is a continuously ongoing process. For the DSO the color information indicates that it may be a dust cloud or a dust-embedded star.

Millimeter to X-ray flares from Sagittarius A*

Context. We report on new simultaneous observations and modeling of the millimeter, near-infrared, and X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the super-massive (4 × 10 6 M� ) black hole at the Galactic center. Aims. We study the applicability of the adiabatic synchrotron source expansion model and study physical processes giving rise to the variable emission of SgrA* from the radio to the X-ray domain. Methods. Our observations were carried out on 18 May 2009 using the NACO adaptive optics (AO) instrument at the European Southern Observatory’s Very Large Telescope, the ACIS-I instrument aboard the Chandra X-ray Observatory, the LABOCA bolometer at the Atacama Pathfinder EXperiment (APEX), and the CARMA mm telescope array at Cedar Flat, California. Results. The X-ray flare had an excess 2−8 keV luminosity between 6 and 12×10 33 erg s −1 . The observations reveal flaring activity in all wavelength bands that can be modeled as the signal from an adiabatically expanding synchrotron self-Compton (SSC) component. Modeling of the light curves shows that the sub-mm follows the NIR emission with a delay of about three-quarters of an hour with an expansion velocity of about vexp ∼ 0.009c. We find source component sizes of around one Schwarzschild radius, flux densities of a few Janskys, and spectral indices α of about + 1( S (ν) ∝ ν −α ). At the start of the flare, the spectra of the two main components peak just short of 1 THz. To statistically explain the observed variability of the (sub-)mm spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and model the flares using a synchrotron and SSC mechanism. Conclusions. These parameters suggest that either the adiabatically expanding source components have a bulk motion larger than vexp or the expanding material contributes to a corona or disk, confined to the immediate surroundings of SgrA*. For the bulk of the synchrotron and SSC models, we find synchrotron turnover frequencies in the range of 300−400 GHz. For the pure synchrotron models, this results in densities of relativistic particles of the order of 10 6.5 cm −3 and for the SSC models, the median densities are about one order of magnitude higher. However, to obtain a realistic description of the frequency-dependent variability amplitude of SgrA*, models with higher turnover frequencies and even higher densities are required.

Monitoring the Dusty S-cluster Object (DSO/G2) on its Orbit toward the Galactic Center Black Hole

We analyze and report in detail new near-infrared (1.45-2.45 ?m) observations of the Dusty S-cluster Object (DSO/G2) during its approach to the black hole at the center of the Galaxy that were carried out with the ESO Very Large Telescope/SINFONI between 2014 February and September. Before 2014 May we detect spatially compact Br? and Pa? line emission from the DSO at about 40 mas east of Sgr A*. The velocity of the source, measured from the redshifted emission, is 2700???60 km s?1. No blueshifted emission above the noise level is detected at the position of Sgr A* or upstream of the presumed orbit. After May we find spatially compact Br? blueshifted line emission from the DSO at about 30 mas west of Sgr A* at a velocity of ?3320???60 km s?1 and no indication for significant redshifted emission. We do not detect any significant extension of the velocity gradient across the source. We find a Br? line FWHM of 50???10 ? before and 15???10 ? after the peribothron transit, i.e., no significant line broadening with respect to last year is observed. Br? line maps show that the bulk of the line emission originates from a region of less than 20 mas diameter. This is consistent with a very compact source on an elliptical orbit with a peribothron time passage in 2014.39???0.14. For the moment, the flaring activity of the black hole in the near-infrared regime has not shown any statistically significant increment. Increased accretion activity of Sgr A* may still be upcoming. We discuss details of a source model according to which the DSO is a young accreting star rather than a coreless gas and dust cloud.

ALMA-backed NIR high resolution integral field spectroscopy of the NUGA galaxy NGC 1433

We present the results of near-infrared (NIR) H- and K-band European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 1433. We present emission and absorption line measurements in the central kpc of NGC 1433. We detect a narrow Balmer line and several H2 lines. We find that the stellar continuum peaks in the optical and NIR in the same position, indicating that there is no covering of the center by a nuclear dust lane. A strong velocity gradient is detected in all emission lines at that position. The position angle of this gradient is at 155\deg whereas the galactic rotation is at a position angle of 201\deg. Our measures of the molecular hydrogen lines, hydrogen recombination lines, and [Feii] indicate that the excitation at the nucleus is caused by thermal excitation, i.e. shocks which can be associated with active galactic nuclei emission, supernovae or outflows. The line ratios [Feii]/Pa{\beta} and H2/Br{\gamma} show a Seyfert to LINER identification of the nucleus. The stellar continuum is dominated by spectral signatures of red-giant M stars. The stellar line-of-sight velocity follows the galactic field whereas the light continuum follows the nuclear bar. The dynamical center of NGC 1433 coincides with the optical and NIR center of the galaxy and the black hole position. Within the central arcsecond, the molecular hydrogen and the 12CO(3-2) emissions - observed in the NIR and in the sub-millimeter with SINFONI and ALMA, respectively - are indicative for a nuclear outflow originating from the galaxys SMBH. A small circum nuclear disk cannot be fully excluded. Derived gravitational torques show that the nuclear bar is able to drive gas inwards to scales where viscosity torques and dynamical friction become important. The black hole mass derived using stellar velocity dispersion is 10^7 M_sun.

The nuclear gas disk of NGC 1566 dissected by SINFONI and ALMA

We present the results of near-infrared (NIR) H- and K-band European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert galaxy NGC 1566. We investigate the central kpc of this nearby galaxy, concentrating on excitation conditions, morphology, and stellar content. NGC 1566 was selected from our NUGA (-south) sample and is a ringed, spiral galaxy with a stellar bar in north-south direction (PA 5 ). The galaxy inhibits a very active Seyfert 1 nucleus but narrow line ratios from optical observations in the nuclear region are similar to Seyfert 2 galaxies. The recent strong activity phase, as inferred from strong variablity in X-ray to IR wavelengths, makes NGC 1566 an ideal candidate to look for feeding and feedback of a supermassive black hole. We present emission and absorption line measurements in the central kpc of NGC 1566. Broad and narrow Br lines were detected. The detection of a broad Br component is a clear sign of a supermassive black hole in the center. Blackbody emission temperatures of 1000 K are indicative of a hot dust component, the torus, in the nuclear region. The molecular hydrogen lines, hydrogen recombination lines, and [Feii] indicate that the excitation at the center is coming from an AGN. The central region is predominantly inhabited by molecular gas, dust, and an old K-M type giant stellar population. The molecular gas and stellar velocity maps both show a rotation pattern. The molecular gas velocity field shows a perturbation toward the center that is typical for bars or spiral density waves. The molecular gas species of warm H2(1 0)S(1) and cold 12 CO(3 2) gas trace a nuclear gas disk of about 3 00 in radius with a nuclear spiral reaching toward the nucleus. From the equivalent width of H2(1 0)S(1) a molecular ring with r . 3 00 can be inferred. This spiral seems to be an instrument that allows gas to fall toward the nucleus down to <50 pc scales. The excitation of molecular hydrogen in the nuclear gas disk is not clear, but diagnostic diagrams show a distinction between the nuclear region and a <9 Myr old star-forming region at the southwestern spiral arm. Gas that might be shocked is detected 2 00 from the center, which is visible in dispersion maps of H2(1 0)S(1) and 12 CO(3 2) and in the 0.87 mm continuum.

Star formation in the vicinity of nuclear black holes: young stellar objects close to Sgr A*

It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black hole. Yet, young stars have been observed across the entire nuclear star cluster of the Milky Way including the region close (

A low-luminosity type-1 QSO sample. V. Overluminous host spheroids and their excitation mechanisms

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A low-luminosity type-1 QSO sample - II. Tracing circumnuclear star formation in HE 1029-1831 with SINFONI

0.5~pc) to the central black hole, Sgr A*. Here, we focus particularly on small groups of young stars, such as IRS 13N located 0.1 pc away from Sgr A*, which is suggested to contain about five embedded massive young stellar objects (

Flare emission from Sagittarius A

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A swirling jet in the quasar 1308+326

1 Myr). We perform three dimensional hydrodynamical simulations to follow the evolution of molecular clumps orbiting about a