Thermal SiO and H<sup>13</sup>CO<sup>+</sup>Line Observations of the Dense Molecular Cloud G0.11−0.11 in the Galactic Center Region

Handa, Toshihiro; Sakano, M.; Naito, Sachio; Hiramatsu, Masaaki; Tsuboi, Masamichi

doi:10.1086/497881

Cited by 41 publications

(48 citation statements)

References 19 publications

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“…We caution that the estimate of the N H of a MC in the GC is strongly dependent on the method used to measure it. For example, for the large G0.13-0.13 molecular complex, two extreme values have been inferred for N H , namely 4 × 10 22 cm −2 (Amo-Baladrón et al 2009, using CS J = 1−0 line) and a much higher value of 10 24 cm −2 (Handa et al 2006, based on the H 13 CO + J = 1−0 line). Finally, we calculated the number of H atoms in the MCs and the value of the optical depth for Thomson scattering (τ T ).…”

Section: Analysis and Resultsmentioning

confidence: 99%

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

Capelli¹,

Warwick²,

Porquet³

et al. 2011

A&A

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Context. Bright Fe-K α line emission at 6.4 keV is a unique characteristic of some of the dense molecular complexes present in the Galactic center region. Whether this X-ray fluorescence is due largely to the irradiation of the clouds by X-ray photons or is, at least in part, the result of cosmic-ray particle bombardment, remains an interesting open question. Aims. We present the results of XMM-Newton observations performed over the last eight years of the region surrounding the Arches cluster in the Galactic center. We study the spatial distribution and temporal behaviour of the Fe-K α emission with the objective of identifying the likely source of the excitation. Methods. We have constructed an Fe-K α fluence map in a narrow energy band of width 128 eV centered on 6.4 keV. We use this to localize the brightest fluorescence features in the vicinity of the Arches cluster. We have investigated the variability of the 6.4-keV line emission of several clouds through spectral fitting of the EPIC MOS data with the use of a modelled background, which avoids many of the systematics inherent in local background subtraction. We also employ spectral stacking of both EPIC PN and MOS data to search for evidence of an Fe-K edge feature imprinted on the underlying X-ray continuum.Results. The lightcurves of the Fe-K α line emission from three bright molecular knots close to the Arches cluster were found to be constant over the 8-year observation window. However, West of the cluster, we found a bright cloud which shows the fastest Fe-K α variability yet seen in a molecular cloud in the Galactic center region. The time averaged spectra of the molecular clouds revealed no convincing evidence of the 7.1-keV edge feature, albeit with only weak constraints. The EW of the 6.4-keV line emitted by the clouds near to the cluster was found to be ∼1.0 keV. Conclusions. The observed Fe-K α line flux and the high value of the EW suggest an origin of the fluorescence in the photoionization of the MCs by X-ray photons, although excitation by cosmic-ray particles is not specifically excluded. For the three clouds nearest to the Arches cluster, the identification of the source of these X-rays as an earlier outburst on Sgr A* is at best tentative, although not entirely ruled out by the observations. On the other hand, the hardness of the nonthermal component associated with the 6.4-keV line emission might be best explained in terms of the bombardment of the clouds by cosmic-ray particles emanating from the Arches cluster itself. The relatively short-timescale variability seen in the 6.4-keV line emission from the cloud to the west of the cluster is most likely the result of its X-ray illumination by a nearby transient X-ray source.

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Section: Analysis and Resultsmentioning

confidence: 99%

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

Capelli¹,

Warwick²,

Porquet³

et al. 2011

A&A

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“…For example, the G0.11-0.11 cloud (our region F) has been the subject of numerous studies over the last decade. Using, respectively, the intensity of the CS and the H 13 CO + emission lines, Amo-Baladrón et al (2009) and Handa et al (2006) measured two extreme values for the N H C of this MC, namely 2 × 10 22 and 10 24 cm −2 , respectively. A better approach is to measure the column density of Fe atoms in the cloud directly from the X-ray spectrum.…”

Section: Column Densities Of the Cloudsmentioning

confidence: 97%

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

Capelli

Warwick

Porquet

et al. 2012

A&A

108

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Context. The spatial distribution and variability of Fe-Kα emission from molecular clouds in the Galactic centre region may provide an important key to the understanding of the recent history of Sgr A*. A very plausible interpretation is that this variability represents an echo in the reflected radiation from the clouds of a past episode of high activity in Sgr A*. Aims. We examine the temporal and spectral properties of nine Fe-Kα bright molecular clouds (three of which newly studied) within about 30 pc of Sgr A*, in order to understand and constrain the primary energising source of the Fe fluorescence. Methods. We collected all the archival XMM-Newton observations targeted at Sgr A*. The variability of the Fe-Kα line at 6.4-keV in specific cloud regions was investigated by spectrally fitting the data derived from the EPIC MOS cameras, after subtracting a modelled background. We have also studied the reflection imprints in time-averaged pn-spectra of each cloud. This involved measuring the equivalent width (EW) of the 6.4 keV line with respect to the underlying scattered continuum and the optical depth of the Fe-K absorption edge at 7.1 keV, superimposed on this same continuum. Finally we stacked the MOS spectra from two extended regions in order to quantify the east-west asymmetry apparent in the low-surface brightness diffuse Fe-Kα line emission. Results. Significant Fe-Kα variability was detected, with a spatial and temporal pattern consistent with that reported in previous studies. The main breakthrough that sets our paper apart from earlier contributions on this topic is the direct measurement of the column density and the Fe abundance of the MCs in our sample. All the spectra were characterised by a high EW of the Fe-Kα line and the presence of absorption at the Fe-K edge, both of which serve as tracers of X-ray illumination. We used the EW measurements to infer the average Fe abundance within the clouds to be 1.6 ± 0.1 times solar. The cloud column densities derived from the spectral analysis were typically of the order of 10 23 cm −2 , which is significantly higher than previous estimates. This in turn has a significant impact on the inferred geometry and time delays within the cloud system. The measured cloud parameters were used to set constraints on the past activity of Sgr A* and to investigate whether a contribution to the Fe fluorescence by cosmic-ray bombardment is plausible. Conclusions. Past X-ray activity of Sgr A* is the most likely source of ionisation within the molecular clouds in the innermost 30 pc of the Galaxy. In this scenario, the X-ray luminosity required to excite these reflection nebulae is of the order of 10 37 -10 38 erg s −1 , significantly lower than that estimated for the Sgr B2 molecular cloud. Moreover, the inferred Sgr A* lightcurve over the past 150 years shows a long-term downwards trend punctuated by occasional counter-trend brightening episodes of at least 5 years duration. Finally, we found that a contribution to the Fe fluorescence by X-ray transient binaries...

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“…GCM −0.13 −0.08 is also known as the 20 km s −1 cloud and is one of the densest clouds in the Sagittarius A (Sgr A) cloud complex (Tsuboi et al 2011). GCM0.11−0.11 is another member of the Sgr A cloud complex that appears to be composed of a composite of hot and dense clumps (Handa et al 2006).…”

Section: Observationsmentioning

confidence: 99%

Uniform Silicon Isotope Ratios Across the Milky Way Galaxy

Monson¹,

Morris²,

Young³

2017

ApJ

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We report the relative abundances of the three stable isotopes of silicon, 28 Si, 29 Si, and 30 Si, across the Galaxy using the v J 0, 1 0 = =  transition of silicon monoxide. The chosen sources represent a range in Galactocentric radii (R GC ) from 0 to 9.8 kpc. The high spectral resolution and sensitivity afforded by the Green Bank Telescope permit isotope ratios to be corrected for optical depths. The optical-depth-corrected data indicate that the secondary-to-primary silicon isotope ratios Si Si 29 28and Si Si 30 28vary much less than predicted on the basis of other stable isotope ratio gradients across the Galaxy. Indeed, there is no detectable variation in Si isotope ratios with R GC . This lack of an isotope ratio gradient stands in stark contrast to the monotonically decreasing trend with R GC exhibited by published secondary-to-primary oxygen isotope ratios. These results, when considered in the context of the expectations for chemical evolution, suggest that the reported oxygen isotope ratio trends, and perhaps those for carbon as well, require further investigation. The methods developed in this study for SiO isotopologue ratio measurements are equally applicable to Galactic oxygen, carbon, and nitrogen isotope ratio measurements, and should prove useful for future observations of these isotope systems.

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Thermal SiO and H¹³CO⁺Line Observations of the Dense Molecular Cloud G0.11−0.11 in the Galactic Center Region

Cited by 41 publications

References 19 publications

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

Uniform Silicon Isotope Ratios Across the Milky Way Galaxy

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Thermal SiO and H13CO+Line Observations of the Dense Molecular Cloud G0.11−0.11 in the Galactic Center Region

Cited by 41 publications

References 19 publications

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

Fe Kαline emission from the Arches cluster region – evidence for ongoing particle bombardment?

The X-ray lightcurve of Sagittarius A* over the past 150 years inferred from Fe-Kαline reverberation in Galactic centre molecular clouds

Uniform Silicon Isotope Ratios Across the Milky Way Galaxy

Contact Info

Product

Resources

About

Thermal SiO and H¹³CO⁺Line Observations of the Dense Molecular Cloud G0.11−0.11 in the Galactic Center Region