Astro arXiv | astro-ph.GA and astro-ph.CO

Corentin Cadiou
  • 0.0 (0)
  • NATURAL SCIENCES
  • UPDATED DAILY

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

  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

    A bias-free cosmological analysis with quasars alleviating H 0 tension

    A bias-free cosmological analysis with quasars alleviating H 0 tension by Aleksander Łukasz Lenart et al. on Wednesday 30 November Cosmological models and their parameters are widely debated because of theoretical and observational mismatches of the standard cosmological model, especially the current discrepancy between the value of the Hubble constant, $H_{0}$, obtained by Type Ia supernovae (SNe Ia), and the Cosmic Microwave Background Radiation (CMB). Thus, considering high-redshift probes like quasars (QSOs), having intermediate redshifts between SNe Ia and CMB, is a necessary step. In this work, we use SNe Ia and the most updated QSO sample, reaching redshifts up to $z\sim7.5$, applying the Risaliti-Lusso QSO relation based on a non-linear relation between ultraviolet and X-ray luminosities. We consider this relation both in its original form and corrected for selection biases and evolution in redshift through a reliable statistical method also accounting for the circularity problem. We also explore two approaches: with and without calibration on SNe Ia. We then investigate flat and non-flat standard cosmological models and a flat $w$CDM model, with a constant dark energy equation of state parameter $w$. Remarkably, when correcting for the evolution as a function of cosmology, we obtain closed constraints on $\Omega_M$ using only non-calibrated QSOs. We find that considering non-calibrated QSOs combined with SNe Ia and accounting for the same correction, our results are compatible with a flat $\Lambda$CDM model with $\Omega_M = 0.3$ and $H_0 = 70 \, \mathrm{km\,s^{-1}\,Mpc^{-1}}$. Intriguingly, the $H_0$ values obtained place halfway between the one from SNe Ia and CMB, paving the way for new insights into the $H_0$ tension. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.10785v2

    1 min

  6. 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

  7. 11/30/2022

    Accelerating BAO Scale Fitting Using Taylor Series

    Accelerating BAO Scale Fitting Using Taylor Series by Matthew Hansen et al. on Wednesday 30 November The Universe is currently undergoing accelerated expansion driven by dark energy. Dark energy's essential nature remains mysterious: one means of revealing it is by measuring the Universe's size at different redshifts. This may be done using the Baryon Acoustic Oscillation (BAO) feature, a standard ruler in the galaxy 2-Point Correlation Function (2PCF). In order to measure the distance scale, one dilates and contracts a template for the 2PCF in a fiducial cosmology, using a scaling factor $\alpha$. The standard method for finding the best-fit $\alpha$ is to compute the likelihood over a grid of roughly 100 values of it. This approach is slow; in this work, we propose a significantly faster way. Our method writes the 2PCF as a polynomial in $\alpha$ by Taylor-expanding it about $\alpha = 1$, exploiting that we know the fiducial cosmology sufficiently well that $\alpha$ is within a few percent of unity. The likelihood resulting from this expansion may then be analytically solved for the best-fit $\alpha$. Our method is 48-85$\times$ faster than a directly comparable approach in which we numerically minimize $\alpha$, and $\sim$$12,000 \times$ faster than the standard iterative method. Our work will be highly enabling for upcoming large-scale structure redshift surveys such as that by Dark Energy Spectroscopic Instrument (DESI). arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2112.06438v2

    1 min

  8. 11/30/2022

    Accelerating BAO Scale Fitting Using Taylor Series

    Accelerating BAO Scale Fitting Using Taylor Series by Matthew Hansen et al. on Wednesday 30 November The Universe is currently undergoing accelerated expansion driven by dark energy. Dark energy's essential nature remains mysterious: one means of revealing it is by measuring the Universe's size at different redshifts. This may be done using the Baryon Acoustic Oscillation (BAO) feature, a standard ruler in the galaxy 2-Point Correlation Function (2PCF). In order to measure the distance scale, one dilates and contracts a template for the 2PCF in a fiducial cosmology, using a scaling factor $\alpha$. The standard method for finding the best-fit $\alpha$ is to compute the likelihood over a grid of roughly 100 values of it. This approach is slow; in this work, we propose a significantly faster way. Our method writes the 2PCF as a polynomial in $\alpha$ by Taylor-expanding it about $\alpha = 1$, exploiting that we know the fiducial cosmology sufficiently well that $\alpha$ is within a few percent of unity. The likelihood resulting from this expansion may then be analytically solved for the best-fit $\alpha$. Our method is 48-85$\times$ faster than a directly comparable approach in which we numerically minimize $\alpha$, and $\sim$$12,000 \times$ faster than the standard iterative method. Our work will be highly enabling for upcoming large-scale structure redshift surveys such as that by Dark Energy Spectroscopic Instrument (DESI). arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2112.06438v2

    1 min
See All (608)

About

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

Information