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Register a new userCAPOS: The bulge Cluster APOgee Survey I. Overview and initial ASPCAP results
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Added by
Jose G. Fernandez-Trincado
Publication date
2021
fields
Physics
and research's language is
English
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Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools. Aims. CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, [{alpha}/Fe], and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs. Methods. CAPOS uses the APOGEE-2S spectrograph observing in the H band to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline. Results. We derive mean [Fe/H] values of $-$0.85$pm$0.04 (Terzan 2), $-$1.40$pm$0.05 (Terzan 4), $-$1.20$pm$0.10 (HP 1), $-$1.40$pm$0.07 (Terzan 9), $-$1.07$pm$0.09 (Djorg 2), $-$1.06$pm$0.06 (NGC 6540), and $-$1.11$pm$0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean [$alpha$/Fe] and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have [Si/Fe] abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances ...
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We present results from a study of fifteen red giant members of the intermediate-metallicity globular cluster (GC) FSR 1758 using high-resolution near-infrared spectra collected with the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2), obtained as part of CAPOS (the bulge Cluster APOgee Survey). Since its very recent discovery as a massive GC in the bulge region, evoking the name Sequoia, this has been an intriguing object with a highly debated origin, and initially led to the suggestion of a purported progenitor dwarf galaxy of the same name. In this work, we use new spectroscopic and astrometric data to provide additional clues to the nature of FSR 1758. Our study confirms the GC nature of FSR 1758, and as such we report for the first time the existence of the characteristic N-C anti-correlation and Al-N correlation, revealing the existence of the multiple-population phenomenon, similar to that observed in virtually all GCs. Furthermore, the presence of a population with strongly enriched aluminium makes it unlikely FSR 1758 is the remnant nucleus of a dwarf galaxy, as Al-enhanced stars are uncommon in dwarf galaxies. We find that FSR 1758 is slightly more metal rich than previously reported in the literature, with a mean metallicity [Fe/H] between $-1.43$ to $-1.36$ (depending on the adopted atmospheric parameters), and with a scatter within observational error, again pointing to its GC nature. Overall, the $alpha$-enrichment ($gtrsim+0.3$ dex), Fe-peak (Fe, Ni), light- (C, N), and odd-Z (Al) elements follow the trend of intermediate-metallicity GCs. ... A new examination of its dynamical properties with the texttt{GravPot16} model favors an association with the Gaia-Enceladus-Sausage accretion event. Thus, paradoxically, the cluster that gave rise to the name of the Sequoia dwarf galaxy does not appear to belong to this specific merging event.
The Blanco Dark Energy Camera (DECam) Bulge survey is a Vera Rubin Observatory (LSST) pathfinder imaging survey, spanning $sim 200$ sq. deg. of the Southern Galactic bulge, $-2^circ <$b$< -13^circ$ and $-11^circ <$l$ < +11^circ$. We have employed the CTIO-4m telescope and the Dark Energy Camera (DECam) to image a contiguous $sim 200$ sq. deg. region of the relatively less reddened Southern Galactic bulge, in SDSS $u$ + Pan-STARRS$grizy$. Optical photometry with its large colour baseline will be used to investigate the age and metallicity distributions of the major structures of the bulge. Included in the survey footprint are 26 globular clusters imaged in all passbands. Over much of the bulge, we have Gaia DR2 matching astrometry to $isim 18$, deep enough to reach the faint end of the red clump. This paper provides the background, scientific case, and description of the survey. We present an array of new reddening-corrected colour-magnitude diagrams that span the extent of Southern Galactic bulge. We argue that a population of massive stars in the blue loop evolutionary phase, proposed to lie in the bulge, are instead at $sim 2$ kpc from the Sun and likely red clump giants in the old disk. A bright red clump near $(l,b)=(+8^circ,-4^circ)$ may be a feature in the foreground disk, or related to the long bar reported in earlier work. We also report the first map of the blue horizontal branch population spanning the BDBS field of regard, and our data does not confirm the reality of a number of proposed globular clusters in the bulge.
The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) project is one of the legacy projects using the new multi-beam FOREST receiver installed on the Nobeyama 45-m telescope. This project aims to investigate the distribution, kinematics, and physical properties of both diffuse and dense molecular gas in the Galaxy at once by observing 12CO, 13CO, and C18O J=1-0 lines simultaneously. The mapping regions are a part of the 1st quadrant (10d < l < 50d, |b| < 1d) and the 3rd quadrant (198d < l <236d, |b| < 1d) of the Galaxy, where spiral arms, bar structure, and the molecular gas ring are included. This survey achieves the highest angular resolution to date (~20) for the Galactic plane survey in the CO J=1-0 lines, which makes it possible to find dense clumps located farther away than the previous surveys. FUGIN will provide us with an invaluable dataset for investigating the physics of the galactic interstellar medium (ISM), particularly the evolution of interstellar gas covering galactic scale structures to the internal structures of giant molecular clouds, such as small filament/clump/core. We present an overview of the FUGIN project, observation plan, and initial results, which reveal wide-field and detailed structures of molecular clouds, such as entangled filaments that have not been obvious in previous surveys, and large-scale kinematics of molecular gas such as spiral arms.
We present methods and results from 21-cm Spectral Line Observations of Neutral Gas with the EVLA (21-SPONGE), a large survey for Galactic neutral hydrogen (HI) absorption with the Karl G. Jansky Very Large Array (VLA). With the upgraded capabilities of the VLA, we reach median root-mean-square (RMS) noise in optical depth of $sigma_{tau}=9times 10^{-4}$ per $0.42rm,km,s^{-1}$ channel for the 31 sources presented here. Upon completion, 21-SPONGE will be the largest HI absorption survey with this high sensitivity. We discuss the observations and data reduction strategies, as well as line fitting techniques. We prove that the VLA bandpass is stable enough to detect broad, shallow lines associated with warm HI, and show that bandpass observations can be combined in time to reduce spectral noise. In combination with matching HI emission profiles from the Arecibo Observatory ($sim3.5$ angular resolution), we estimate excitation (or spin) temperatures ($rm T_s$) and column densities for Gaussian components fitted to sightlines along which we detect HI absorption (30/31). We measure temperatures up to $rm T_ssim1500rm,K$ for individual lines, showing that we can probe the thermally unstable interstellar medium (ISM) directly. However, we detect fewer of these thermally unstable components than expected from previous observational studies. We probe a wide range in column density between $sim10^{16}$ and $>10^{21}rm,cm^{-2}$ for individual HI clouds. In addition, we reproduce the trend between cold gas fraction and average $rm T_s$ found by synthetic observations of a hydrodynamic ISM simulation by Kim et al. (2014). Finally, we investigate methods for estimating HI $rm T_s$ and discuss their biases.
We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15<log N(HI)<19 at z<1 using the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our main aim is to determine the metallicity distribution of these absorbers. Our sample consists of 224 absorbers selected on the basis of their HI absorption strength. Here we discuss the properties of our survey and the immediate empirical results. We find singly and doubly ionized metal species and HI typically have similar velocity profiles, implying they probe gas in the same or similar environments. The column density ionic ratios (e.g., CII/CIII, OI/CII) indicate the gas in these absorbers is largely ionized, and the ionization conditions are quite comparable across the sampled N(HI) range. The Doppler parameters of the HI imply T<50,000 K on average, consistent with the gas being photoionized. The MgII column densities span >2 orders of magnitude at any given N(HI), indicating a wide range of metallicities (from solar to <1/100 solar). In the range 16.2<log N(HI)<17, there is a gap in the N(MgII) distribution corresponding to gas with ~10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying truly-pristine gas at z<1 is uncommon. We find [FeII/MgII] = -0.4+/-0.3, and since alpha-enhancement can affect this ratio, dust depletion is extremely mild.
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