scholarly journals The Herschel view of the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 1-14
Author(s):  
John Bally ◽  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Center ◽  
Galactic Plane ◽  
Formation Rate ◽  
Asymmetric Distribution ◽  
The Galaxy ◽  
Sgr A ◽  
Almost All

AbstractThe 3.5 meter diameter Herschel Space Observatory conducted a ∼720 square-degree survey of the Galactic plane, the Herschel Galactic plane survey (Hi-GAL). These data provide the most sensitive and highest resolution observations of the far-IR to sub-mm continuum from the central molecular zone (CMZ) at λ = 70, 160, 250, 350, and 500 μm obtained to date. Hi-GAL can be used to map the distributions of temperature and column density of dust in CMZ clouds, warm dust in Hii regions, and identify highly embedded massive protostars and clusters and the dusty shells ejected by supergiant stars. These data enable classification of sources and re-evaluation of the current and recent star-formation rate in the CMZ. The outer CMZ beyond |l| = 0.9 degrees (Rgal > 130 pc) contains most of the dense (n > 104 cm−3 gas in the Galaxy but supports very little star formation. The Hi-GAL and Spitzer data show that almost all star formation occurs in clouds moving on x2 orbits at Rgal < 100 pc. While the 106 M⊙ Sgr B2 complex, the 50 km s−1 cloud near Sgr A, and the Sgr C region are forming clusters of massive stars, other clouds are relatively inactive star formers, despite their high densities, large masses, and compact sizes. The asymmetric distribution of dense gas about Sgr A* on degree scales (most dense CMZ gas and dust is at positive Galactic longitudes and positive VLSR) and compact 24 μm sources (most are at negative longitudes) may indicate that eposidic mini-starbursts occasionally ‘blow-out’ a portion of the gas on these x2 orbits. The resulting massive-star feedback may fuel the compact 30 pc scale Galactic center bubble associated with the Arches and Quintuplet clusters, the several hundred pc scale Sofue-Handa lobe, and the kpc-scale Fermi/LAT bubble, making it the largest ‘superbubble’ in the Galaxy. A consequence of this model is that in our Galaxy, instead of the supermassive black hole (SMBH) limiting star formation, star formation may limit the growth of the SMBH.

scholarly journals 7.13. The Sgr A East HII complex and associated features

1998 ◽  
Vol 184 ◽  
pp. 317-318 ◽  
Author(s):  
Keven I. Uchida ◽  
Mark R. Morris ◽  
Gene Serabyn ◽  
David Fong ◽  
Thomas Meseroll
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Center ◽  
Galactic Plane ◽  
Alternative Hypothesis ◽  
Rapid Expansion ◽  
H Ii Regions ◽  
Expansion Time ◽  
Sgr A ◽  
Relativistic Particles

The Sgr A East H ii complex consists of 4 compact H ii regions situated just east of and following, in an arc pattern, the edge of the Sgr A East nonthermal shell. Located between the arc of H ii regions and the nonthermal shell is a dense molecular ridge – presumably compressed – known as the “50 km/s cloud”. The hypothesis that these H ii regions delineate massive star formation provoked by the rapid expansion of Sgr A East into the molecular cloud is problematical because of the mismatch of the shell expansion and star formation time scales. We therefore examine the alternative hypothesis that Sgr A East is a quasi-static or slowly expanding structure fed from within by the release of relativistic particles from sources at or near the nucleus. The elongation of SgrA East along the Galactic plane is ascribed to the shear inherent in the velocity field this close to the Galactic center (GC). In this proceeding we discuss our ongoing efforts to model the effects of shear in detail, using the elongation of Sgr A East to constrain its expansion time scale.

scholarly journals Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S248) ◽  
pp. 141-147 ◽  
Author(s):  
M. J. Reid
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Proper Motions ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Trigonometric Parallaxes ◽  
Sgr A ◽  
Definition Of ◽  
Almost All

AbstractThe VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

scholarly journals Feeding and feedback in nearby AGN – comparison with the Milky Way center

2013 ◽  
Vol 9 (S303) ◽  
pp. 354-363 ◽  
Author(s):  
T. Storchi-Bergmann
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Center ◽  
Formation Rate ◽  
Activity Cycle ◽  
Nuclear Region ◽  
Nuclear Activity ◽  
The Galaxy ◽  
Mass Outflow ◽  
Sgr A

AbstractI discuss feeding and feedback processes observed in the inner few hundred parsecs of nearby active galaxies using integral field spectroscopy at spatial resolutions of a few to tens of parsecs. Signatures of feedback include outflows from the nucleus with velocities ranging from 200 to 1000 km s−1, with mass outflow rates between 0.5 and a few M⊙ yr−1. Signatures of feeding include the observation of gas inflows along nuclear spirals and filaments, with velocities ranging from 50 to 100 km s−1 and mass flow rates from 0.1 to ∼1 M⊙ yr−1. These rates are 2–3 orders of magnitude larger than the mass accretion rate to the supermassive black hole (SMBH). These inflows can thus lead, during less than one activity cycle, to the accumulation of enough gas in the inner few hundred parsecs, to trigger the formation of new stars, leading to the growth of the galaxy bulge. Young to intermediate age stars have indeed been found in circumnuclear rings around a number of Active Galactic Nuclei (AGN). In particular, one of these rings, with radius of ≈ 100 pc is observed in the Seyfert 2 galaxy NGC 1068, and is associated to an off-centered molecular ring, very similar to that observed in the Milky Way (MW). On the basis of an evolutionary scenario in which gas falling into the nuclear region triggers star formation followed by the triggering of nuclear activity, we speculate that, in the case of the MW, molecular gas has already accumulated within the inner ≈ 100 pc to trigger the formation of new stars, as supported by the presence of blue stars close to the galactic center. A possible increase in the star-formation rate in the nuclear region will then be followed, probably tens of millions of years later, by the triggering of nuclear activity in Sgr A*.

scholarly journals Interactions and star formation

2015 ◽  
Vol 11 (S315) ◽  
pp. 236-239
Author(s):  
Johan H. Knapen ◽  
Mauricio Cisternas ◽  
Miguel Querejeta
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Morphological Type ◽  
Stellar Mass ◽  
Interacting Galaxies ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Ir Emission

AbstractWe investigate the influence of interactions on the star formation by studying a sample of almost 1500 of the nearest galaxies, all within a distance of ~45 Mpc. We define the massive star formation rate (SFR), as measured from far-IR emission, and the specific star formation rate (SSFR), which is the former quantity normalized by the stellar mass of the galaxy, and explore their distribution with morphological type and with stellar mass. We then calculate the relative enhancement of these quantities for each galaxy by normalizing them by the median SFR and SSFR values of individual control populations of similar non-interacting galaxies. We find that both SFR and SSFR are enhanced in interacting galaxies, and more so as the degree of interaction is higher. The increase is, however, moderate, reaching a maximum of a factor of 1.9 for the highest degree of interaction (mergers). The SFR and SSFR are enhanced statistically in the population, but in most individual interacting galaxies they are not enhanced at all. We discuss how those galaxies with the largest SFR and/or SSFR enhancement can be defined as starbursts. We argue that this study, based on a representative sample of nearby galaxies, should be used to place constraints on studies based on samples of galaxies at larger distances.

scholarly journals Mapping the Galactic Center

1996 ◽  
Vol 171 ◽  
pp. 369-369
Author(s):  
W.J. Duschl ◽  
S. von Linden ◽  
T. Walter ◽  
M. Wittkowski
Keyword(s):  
Angular Momentum ◽  
Molecular Clouds ◽  
Vertical Structure ◽  
Galactic Center ◽  
Galactic Plane ◽  
The Galaxy ◽  
Sgr A ◽  
Celestial Sphere ◽  
Inner Region ◽  
Galactic Longitude

Gas and dust in the inner region of the Galaxy are distributed in a flat, disklike structure. We model the dynamics of this material in the framework of an accretion disk approach, and thus determine the efficiency of the radial transport of mass and angular momentum in the inner ∼ 200 pc of the Galactic Plane. Moreover, this allows us to establish the location (coordinates: galactic longitude l and depth normal to the celestial sphere) of molecular clouds from the observed positions (l) and radial velocities (currently, we neglect details of the vertical structure). Ultimately this will yield a map of the distribution of molecular clouds about Sgr A∗.

scholarly journals MASSIVE STAR FORMATION OF THE SGR A EAST H II REGIONS NEAR THE GALACTIC CENTER

2010 ◽  
Vol 725 (2) ◽  
pp. 1429-1439 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
J. H. Lacy ◽  
M. Wardle ◽  
B. Whitney ◽  
H. Bushouse ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Center ◽  
H Ii Regions ◽  
Massive Star Formation ◽  
Sgr A

scholarly journals 4.8. Distribution of C18O and HNCO emission in the Sagittarius B2 molecular cloud

1998 ◽  
Vol 184 ◽  
pp. 181-182 ◽  
Author(s):  
Fumio Sato ◽  
Tetsuo Hasegawa ◽  
John B. Whiteoak ◽  
Masayoshi Shimizu
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Massive Star ◽  
Galactic Center ◽  
Full Description ◽  
Massive Star Formation ◽  
Hii Region ◽  
The Galaxy ◽  
Molecular Lines ◽  
Star Formation Regions

Sgr B2, located at a distance of ∼100 pc from the Galactic center, is one of the most active, recent massive-star formation regions in the Galaxy. Based on the 13CO (J = 1–0) line data taken with the Nobeyama 45 m telescope, we presented a cloud collision scenario as the triggering mechanism of the burst of massive-star formation there (Hasegawa et al. 1994). In order to obtain further evidence supporting our model, we observed the Sgr B2 molecular cloud in various molecular lines with the 45 m telescope in 1992 February. Twelve points each with 20″ spacings were observed along several strips 3.67′ long at constant galactic longitudes through the major HII region complexes. Here we report the results of the two lines in the 110 GHz band, C18O (J = 1–0) and HNCO (50,5–40,4). Full description of the observations will be given elsewhere (Sato et al. 1997).

scholarly journals Conversion of gas into stars in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 132-138
Author(s):  
S. N. Longmore
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Galactic Center ◽  
High Redshift ◽  
Formation Rate ◽  
Extreme Environment ◽  
Time Interval ◽  
Supermassive Black Hole ◽  
Mass Assembly ◽  
Sgr A

AbstractThe star formation rate in the central 500 pc of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. I discuss which physical mechanisms could be causing this observation and put forward a self-consistent cycle of star formation in the Galactic center, in which the plausible star formation inhibitors are combined. Their ubiquity suggests that the perception of a lowered central SFR should be a common phenomenon in other galaxies with direct implications for galactic star formation and also potentially supermassive black hole growth. I then describe a scenario to explain the presence of super star clusters in the Galactic center environment, in which their formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time. I outline the first results from detailed numerical simulations testing this scenario. Finally, I describe a study showing that in terms of the baryonic composition, kinematics, and densities, the gas in the Galactic center is indistinguishable from high-redshift clouds and galaxies. As such, the Galactic center clouds may be used as a template to understand the evolution (and possibly the life cycle) of high-redshift clouds and galaxies.

scholarly journals Masers and Galactic structure: Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S242) ◽  
pp. 348-355 ◽  
Author(s):  
M. J. Reid ◽  
A. Brunthaler ◽  
K. M. Menten ◽  
Xu Ye ◽  
Zheng Xing-Wu ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Galactic Plane ◽  
Infrared Images ◽  
Star Forming ◽  
Supermassive Black Hole ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Trigonometric Parallaxes ◽  
Sgr A

AbstractAstrometric observations with the VLBA with accuracies approaching ~ 10 μas are being conducted in order to better understand the Galaxy. The location of Sgr A* on infrared images can be determined with an accuracy of a few mas, using stars with SiO maser emission as a calibration grid for infrared images. The apparent proper motion of Sgr A*, which is dominated by the effects of the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0R0 and offers a dynamical definition of the Galactic plane with Sgr A* at its origin. The intrinsic motion of Sgr A* is very small and comparable to that expected for a supermassive black hole. When combined with infrared results, this provides overwhelming evidence that Sgr A* is a supermassive black hole. Finally, we are engaged in a large project to map the spiral structure and kinematics of the Galaxy. Preliminary trigonometric parallaxes, obtained with the VLBA, to eight massive star forming regions are presented.

scholarly journals Massive stars and the creation of our Galactic Center

2003 ◽  
Vol 212 ◽  
pp. 487-496 ◽  
Author(s):  
Donald F. Figer
Keyword(s):  
Star Formation ◽  
Galactic Center ◽  
Massive Stars ◽  
Formation Rate ◽  
Stellar Content ◽  
The Past ◽  
Luminosity Functions ◽  
Region I ◽  
The Galaxy ◽  
Massive Clusters

Our Galactic Center hosts over 10% of the known massive stars in the Galaxy. The majority of these stars are located in three particularly massive clusters that formed within the past 5 Myr. While these clusters are extraordinary, their formation repesents about half of the total inferred star-formation rate in the Galactic Center. There is mounting evidence that the clusters are just present-day examples of the hundreds of such similar clusters that must have been created in the past, and whose stars now comprise the bulk of all stars seen in the region. I discuss the massive stellar content in the Galactic Center and present a new analysis that suggests that effects of continuous star-formation in the Galactic Center can be seen in the observed luminosity functions newly-obtained HST-nicmos and Gemini-ao data.

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