Astro arXiv | astro-ph.GA

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Astro arXiv | astro-ph.GA

Daily Astro papers on the arXiv in astro-ph.GA.

  1. 11/30/2022

    A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane

    A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane by Felix J. Lockman et al. on Wednesday 30 November We have identified a new structure in the Milky Way: a leading component of the Smith high velocity cloud that is now crossing the Galactic plane near longitude 25 degrees. Using new 21cm HI data from the Green Bank Telescope (GBT) we measured the properties of several dozen clouds that are part of this structure. Their kinematics is consistent with that of the Smith Cloud with a VLSR exceeding that permitted by circular rotation in their direction. Most of the clouds in the Leading Component show evidence that they are interacting with disk gas allowing the location of the interaction to be estimated. The Leading Component crosses the Galactic plane at a distance from the Sun of 9.5 kpc, about 4.5 kpc from the Galactic Center. Its HI mass may be as high as 10^6 Solar masses, comparable to the mass of the neutral component of the Smith Cloud, but only a fraction of this is contained in clouds that are resolved in the GBT data. Like the Smith Cloud, the Leading Component appears to be adding mass and angular momentum to the ISM in the inner Galaxy. We suggest that the Smith Cloud is not an isolated object, but rather part of a structure that stretches more than 40 degrees (about 7 kpc) across the sky, in two pieces separated by a gap of about 1 kpc. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.16598v1

    1 min

  2. 11/30/2022

    A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane

    A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane by Felix J. Lockman et al. on Wednesday 30 November We have identified a new structure in the Milky Way: a leading component of the Smith high velocity cloud that is now crossing the Galactic plane near longitude 25 degrees. Using new 21cm HI data from the Green Bank Telescope (GBT) we measured the properties of several dozen clouds that are part of this structure. Their kinematics is consistent with that of the Smith Cloud with a VLSR exceeding that permitted by circular rotation in their direction. Most of the clouds in the Leading Component show evidence that they are interacting with disk gas allowing the location of the interaction to be estimated. The Leading Component crosses the Galactic plane at a distance from the Sun of 9.5 kpc, about 4.5 kpc from the Galactic Center. Its HI mass may be as high as 10^6 Solar masses, comparable to the mass of the neutral component of the Smith Cloud, but only a fraction of this is contained in clouds that are resolved in the GBT data. Like the Smith Cloud, the Leading Component appears to be adding mass and angular momentum to the ISM in the inner Galaxy. We suggest that the Smith Cloud is not an isolated object, but rather part of a structure that stretches more than 40 degrees (about 7 kpc) across the sky, in two pieces separated by a gap of about 1 kpc. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.16598v1

    1 min

  3. 11/30/2022

    A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy

    A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy by Vedant Chandra et al. on Wednesday 30 November We report the discovery of Specter, a disrupted ultrafaint dwarf galaxy revealed by the H3 Spectroscopic Survey. We detected this structure via a pair of comoving metal-poor stars at a distance of 12.5 kpc, and further characterized it with Gaia astrometry and follow-up spectroscopy. Specter is a $25^\circ \times 1^\circ$ stream of stars that is entirely invisible until strict kinematic cuts are applied to remove the Galactic foreground. The spectroscopic members suggest a stellar age $\tau \gtrsim 12$ Gyr and a mean metallicity $\langle\text{[Fe/H]}\rangle = -1.84_{-0.18}^{+0.16}$, with a significant intrinsic metallicity dispersion $\sigma_{ \text{[Fe/H]}} = 0.37_{-0.13}^{+0.21}$. We therefore argue that Specter is the disrupted remnant of an ancient dwarf galaxy. With an integrated luminosity $M_{\text{V}} \approx -2.6$, Specter is by far the least-luminous dwarf galaxy stream known. We estimate that dozens of similar streams are lurking below the detection threshold of current search techniques, and conclude that spectroscopic surveys offer a novel means to identify extremely low surface brightness structures. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2207.13717v2

    1 min

  4. 11/30/2022

    A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy

    A Ghost in Boötes: The Least Luminous Disrupted Dwarf Galaxy by Vedant Chandra et al. on Wednesday 30 November We report the discovery of Specter, a disrupted ultrafaint dwarf galaxy revealed by the H3 Spectroscopic Survey. We detected this structure via a pair of comoving metal-poor stars at a distance of 12.5 kpc, and further characterized it with Gaia astrometry and follow-up spectroscopy. Specter is a $25^\circ \times 1^\circ$ stream of stars that is entirely invisible until strict kinematic cuts are applied to remove the Galactic foreground. The spectroscopic members suggest a stellar age $\tau \gtrsim 12$ Gyr and a mean metallicity $\langle\text{[Fe/H]}\rangle = -1.84_{-0.18}^{+0.16}$, with a significant intrinsic metallicity dispersion $\sigma_{ \text{[Fe/H]}} = 0.37_{-0.13}^{+0.21}$. We therefore argue that Specter is the disrupted remnant of an ancient dwarf galaxy. With an integrated luminosity $M_{\text{V}} \approx -2.6$, Specter is by far the least-luminous dwarf galaxy stream known. We estimate that dozens of similar streams are lurking below the detection threshold of current search techniques, and conclude that spectroscopic surveys offer a novel means to identify extremely low surface brightness structures. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2207.13717v2

    1 min

  5. 11/30/2022

    ALMACAL IX: multi-band ALMA survey for dusty star-forming galaxies and the resolved fractions of the cosmic infrared background

    ALMACAL IX: multi-band ALMA survey for dusty star-forming galaxies and the resolved fractions of the cosmic infrared background by Jianhang Chen et al. on Wednesday 30 November Wide, deep, blind continuum surveys at submillimetre/millimetre (submm/mm) wavelengths are required to provide a full inventory of the dusty, distant Universe. However, conducting such surveys to the necessary depth, with sub-arcsec angular resolution, is prohibitively time-consuming, even for the most advanced submm/mm telescopes. Here, we report the most recent results from the ALMACAL project, which exploits the 'free' calibration data from the Atacama Large Millimetre/submillimetre Array (ALMA) to map the lines of sight towards and beyond the ALMA calibrators. ALMACAL has now covered 1,001 calibrators, with a total sky coverage around 0.3 deg2, distributed across the sky accessible from the Atacama desert, and has accumulated more than 1,000h of integration. The depth reached by combining multiple visits to each field makes ALMACAL capable of searching for faint, dusty, star-forming galaxies (DSFGs), with detections at multiple frequencies to constrain the emission mechanism. Based on the most up-to-date ALMACAL database, we report the detection of 186 DSFGs with flux densities down to S870um ~ 0.2mJy, comparable with existing ALMA large surveys but less susceptible to cosmic variance. We report the number counts at five wavelengths between 870um and 3mm, in ALMA bands 3, 4, 5, 6 and 7, providing a benchmark for models of galaxy formation and evolution. By integrating the observed number counts and the best-fitting functions, we also present the resolved fraction of the cosmic infrared background (CIB) and the CIB spectral shape. Combining existing surveys, ALMA has currently resolved about half of the CIB in the submm/mm regime. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2210.09329v2

    1 min

  6. 11/30/2022

    Assessing the physical reality of Milky Way open cluster candidates

    Assessing the physical reality of Milky Way open cluster candidates by A. E. Piatti et al. on Wednesday 30 November We report results on the analysis of eleven new Milky Way open cluster candidates, recently discovered from the detection of stellar overdensities in the Vector Point diagram, by employing extreme deconvolution Gaussian mixture models. We treated these objects as real open clusters and derived their fundamental properties with their associated intrinsic dispersions by exploring the parameter space through the minimization of likelihood functions on generated synthetic colour-magnitude diagrams (CMDs). The intrinsic dispersions of the resulting ages turned out to be much larger than those usually obtained for open clusters. Indeed, they resemble those of ages and metallicities of composite star field populations. We also traced their stellar number density profiles and mass functions, derived their total masses, Jacobi and tidal radii, which helped us as criteria while assessing their physical nature as real open clusters. Because the eleven candidates show a clear gathering of stars in the proper motion plane and some hint for similar distances, we concluded that they are possibly sparse groups of stars. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15483v1

    1 min

  7. 11/30/2022

    Bar formation in submaximal disks: a challenge for Λ CDM

    Bar formation in submaximal disks: a challenge for Λ CDM by Tahere Kashfi et al. on Wednesday 30 November Bar formation in cosmological simulations of galaxy formation remains challenging. It was previously shown that the fraction of barred galaxies at low stellar masses ($M_*10^{10.5} M_\odot$) in TNG50 is too low compared to observations. Here, we highlight another tension, also observed at higher stellar masses, namely that barred galaxies in TNG50 appear to be maximal disks, in the sense that the majority of the gravitational acceleration is accounted for by baryons at the peak radius of the baryonic rotation curve, while observations account for a substantial fraction of barred submaximal disks. In this letter, we compare the barred fraction of submaximal disks in the local Universe from the SPARC catalogue with that in the TNG50 simulation. We show that, although SPARC tends to select against barred galaxies, the fraction of barred submaximal disks in this dataset is significantly larger than in TNG50. This result adds to the list of challenges related to predicting the right statistics and properties of barred galaxies in $\Lambda$CDM simulations of galaxy formation. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15599v1

    13 sec

  8. 11/30/2022

    Chemical abundances in the dwarf galaxy NGC 4163 based on the nebular and auroral emission lines

    Chemical abundances in the dwarf galaxy NGC 4163 based on the nebular and auroral emission lines by I. A. Zinchenko et al. on Wednesday 30 November We constructed an oxygen abundance map and N/O ratio map of the unusually low excitation dwarf irregular galaxy NGC 4163 based on publicly available spectroscopy obtained by the MaNGA survey. We detected auroral emission line [OII]$\lambda\lambda$7320,7330 which allows us to measure chemical abundance by direct T$_e$ method. We found that the scatter of the oxygen abundance derived by the strong line method is large. The oxygen abundances 12 + log(O/H) derived by strong line method vary from ~7.3 to ~7.8 with a mean value of ~7.55. The oxygen abundances derived in two apertures of 2 arcseconds by the direct T$_e$ method using our measurements of the O$^+$ auroral line is about 7.8 dex. The nitrogen-to-oxygen ratio log(N/O) of about -1.5 is typical value for a low metallicity galaxy, maybe slightly shifted towards higher N/O ratios with respect to the N/O values in the HII regions in nearby galaxies. An unusual negative trend between log(N/O) and oxygen abundance is detected. NGC 4163 is a gas-poor galaxy with a neutral atomic gas mass fraction of around 0.25. The oxygen abundance in the galaxy is only around 0.1 of the oxygen abundance potentially attainable in a galaxy with such a gas mass fraction. The low metallicity coupled with the low gas mass fraction implies that either the metallicity of the interstellar medium of the galaxy was reduced by pristine gas infall in the recent epoch or the evolution of this galaxy was accompanied by strong galactic winds. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15710v1

    1 min
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Daily Astro papers on the arXiv in astro-ph.GA.

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    Astro arXiv
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    Corentin Cadiou
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    © Copyright (c) 2022 Corentin Cadiou and University College London
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