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Register a new userAbsorption Line Survey of H3+ toward the Galactic Center Sources I. GCS 3-2 and GC IRS3
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M. Goto
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We present high-resolution (R = 20000) spectroscopy of H3+ absorption toward the luminous Galactic center sources GCS 3-2 and GC IRS 3. With the efficient wavelength coverage afforded by Subaru IRCS, six absorption lines of H3+ have been detected in each source from 3.5 to 4.0 um, three of which are new. In particular the 3.543 um absorption line of the R(3, 3)^l transition arising from the metastable (J, K) = (3, 3) state has been tentatively detected for the first time in the interstellar medium, where previous observations of H3+ had been limited to absorption lines from the lowest levels: (J, K) = (1, 0) of ortho-H3+ and (1, 1) of para-H3+. The H3+ absorption toward the Galactic center takes place in dense and diffuse clouds along the line of sight as well as the molecular complex close to the Galactic nucleus. At least four kinematic components are found in the H3+ absorption lines. We suggest identifications of the velocity components with those of HI, CO, and H2CO previously reported from radio and infrared observations. H3+ components with velocities that match those of weak and sharp CO and H2CO lines are attributed to diffuse clouds. Our observation has revealed a striking difference between the absorption profiles of H3+ and CO, demonstrating that the spectroscopy of H3+ provides information complementary to that obtained from CO spectroscopy. The tentative detection of the R(3, 3)^l line and the non-detection of spectral lines from other J > 1 levels provide observational evidence for the metastability of the (3, 3) level, which is theoretically expected. This suggests that other metastable J = K levels with higher J may also be populated.
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Infrared absorption lines of H3+, including the metastable R(3,3)l line, have been observed toward eight bright infrared sources associated with hot and massive stars located in and between the Galactic Center Cluster and the Quintuplet Cluster 30 pc to the east. The absorption lines with high velocity dispersion arise in the Galaxys Central Molecular Zone (CMZ) as well as in foreground spiral arms. The temperature and density of the gas in the CMZ, as determined from the relative strengths of the H3+ lines, are T=200-300K and n=50-200cm^-3. The detection of high column densities of H3+ toward all eight stars implies that this warm and diffuse gaseous environment is widespread in the CMZ. The products of the ionization rate and path length for these sight lines are 1000 and 10 times higher than in dense and diffuse clouds in the Galactic disk, respectively, indicating that the ionization rate, zeta, is not less than 10^-15 s^-1 and that L is at least on the order of 50 pc. The warm and diffuse gas is an important component of the CMZ, in addition to the three previously known gaseous environments: (1) cold molecular clouds observed by radio emission of CO and other molecules, (2) hot (T=10^4-10^6K) and highly ionized diffuse gas (n_e=10-100cm^-3) seen in radio recombination lines, far infrared atomic lines, and radio-wave scattering, and (3) ultra-hot (T=10^7-10^8K) X-ray emitting plasma. Its prevalence significantly changes the understanding of the environment of the CMZ. The sight line toward GC IRS 3 is unique in showing an additional H3+ absorption component, which is interpreted as due to either a cloud associated with circumnuclear disk or the 50 km s^-1 cloud known from radio observations. An infrared pumping scheme is examined as a mechanism to populate the (3,3) metastable level in this cloud.
We present follow-up observations to those of Geballe & Oka (2010), who found high column densities of H3+ ~100 pc off of the Galactic center (GC) on the lines of sight to 2MASS J17432173-2951430 (J1743) and 2MASS J17470898-2829561 (J1747). The wavelength coverages on these sightlines have been extended in order to observe two key transitions of H3+, R(3,3)l and R(2,2)l, that constrain the temperatures and densities of the environments. The profiles of the H3+ R(3,3)l line, which is due only to gas in the GC, closely matches the differences between the H3+ R(1,1)l and CO line profiles, just as it does for previously studied sightlines in the GC. Absorption in the R(2,2)l line of H3+ is present in J1747 at velocities between -60 and +100 km/s. This is the second clear detection of this line in the interstellar medium after GCIRS 3 in the Central Cluster. The temperature of the absorbing gas in this velocity range is 350 K, significantly warmer than in the diffuse clouds in other parts of the Central Molecular Zone. This indicates that the absorbing gas is local to Sgr B molecular cloud complex. The warm and diffuse gas revealed by Oka et al. (2005) apparently extends to ~100 pc, but there is a hint that its temperature is somewhat lower in the line of sight to J1743 than elsewhere in the GC. The observation of H3+ toward J1747 is compared with the recent Herschel observation of H2O+ toward Sgr B2 and their chemical relationship and remarkably similar velocity profiles are discussed.
We present a catalogue of candidate H{alpha} emission and absorption line sources and blue objects in the Galactic Bulge Survey (GBS) region. We use a point source catalogue of the GBS fields (two strips of (l x b) = (6 x 1) degrees centred at b = 1.5 above and below the Galactic centre), covering the magnitude range 16 < r < 22.5. We utilize (r-i, r-H{alpha}) colour-colour diagrams to select H{alpha} emission and absorption line candidates, and also identify blue objects (compared to field stars) using the r-i colour index. We identify 1337 H{alpha} emission line candidates and 336 H{alpha} absorption line candidates. These catalogues likely contain a plethora of sources, ranging from active (binary) stars, early-type emission line objects, cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs) to background active galactic nuclei (AGN). The 389 blue objects we identify are likely systems containing a compact object, such as CVs, planetary nebulae and LMXBs. Hot subluminous dwarfs (sdO/B stars) are also expected to be found as blue outliers. Crossmatching our outliers with the GBS X-ray catalogue yields sixteen sources, including seven (magnetic) CVs and one qLMXB candidate among the emission line candidates, and one background AGN for the absorption line candidates. One of the blue outliers is a high state AM CVn system. Spectroscopic observations combined with the multi-wavelength coverage of this area, including X-ray, ultraviolet and (time-resolved) optical and infrared observations, can be used to further constrain the nature of individual sources.
The presence of dark matter is nowadays widely supported by a large body of astronomical and cosmological observations. A large amount of dark matter is expected to be present in the central region of the Milky Way. Very-high-energy (>100 GeV) {gamma}-rays can be produced in the annihilation of dark matter particles. The H.E.S.S. array of Imaging Atmospheric Cherenkov Telescopes is a powerful tools to observe the Galactic Centre trying to detect {gamma}-rays from dark matter annihilation. A new search for a dark matter signal has been carried out on the full H.E.S.S.-I data set of 2004-2014 observations. A 2D-binned likelihood method has been applied to exploit the spectral and spatial properties of signal and background. Updated constraints are derived on the velocity-weighted annihilation cross section for signals from prompt annihilation of dark matter particles into two photons. The larger statistics from the 10-year Galactic Center dataset of H.E.S.S.-I together with the 2D-analysis technique allows to significantly improve the previous limits.
Upon commissioning on Gemini South, FLAMINGOS-2 will be one of the most powerful wide-field near-infrared imagers and multi-object spectrographs ever built for use on 8-meter-class telescopes. In order to take best advantage of the strengths of FLAMINGOS-2 early in its life cycle, the instrument team has proposed to use 21 nights of Gemini guaranteed time in 3 surveys -- the FLAMINGOS-2 Early Science Surveys (F2ESS). The F2ESS will encompass 3 corresponding science themes -- the Galactic Center, galaxy evolution, and star formation. In this paper, I review the design performance and status of FLAMINGOS-2, and describe the planned FLAMINGOS-2 Galactic Center Survey.
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