scholarly journals High spin temperatures at large impact parameters: Ionisation in the outskirts of galaxies

2020 ◽  
Vol 635 ◽  
pp. A166
Author(s):  
S. J. Curran
Keyword(s):  
Temperature Distribution ◽  
High Resolution ◽  
Impact Parameter ◽  
Column Density ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Spin Temperature ◽  
The Mean ◽  
Impact Parameters

By including the most recent observations of H I 21-cm absorption through nearby galactic discs, we confirm our previous assertion that there is an anti-correlation between the abundance of cool neutral atomic gas and impact parameter. In comparing the measured neutral hydrogen column densities of the sample with the absorption strength, we find a peak in the mean spin temperature of ⟨Tspin/f ⟩ ≈ 2310 K at an impact parameter of ρ ≈ 14 kpc, with ⟨Tspin/f ⟩≳1000 K in the remainder of the disc. This is significantly different to the spin temperature distribution in the Milky Way, which exhibits a constant ≈250 − 400 K over ρ = 8 − 25 kpc. The measured column densities may, however, suffer from beam dilution, which we show appears to be the case for the observations of H I 21-cm emission in which the beam subtends radii of ≳10 kpc. We therefore applied the column density profile of the Milky Way, in addition to the mean of the sample, observed at sufficiently high resolution, and the mean profile for the nearby ∼1012 M⊙ galaxies in the IllustrisTNG simulations. All of the models yield a peak in the mean spin temperature at similar impact parameters (r ≈ 10 − 15 kpc) as the measured column densities. These radii are similar to those of the spiral arms where H II regions are often concentrated. We therefore suggest that the elevated spin temperatures trace the H II regions observed in the outer disc of many spiral galaxies.

scholarly journals Influence of Gravitational Lensing on Estimates of Ω in Neutral Hydrogen

1996 ◽  
Vol 173 ◽  
pp. 97-98
Author(s):  
Matthias Bartelmann ◽  
Abraham Loeb
Keyword(s):  
Observational Data ◽  
Gravitational Lensing ◽  
Column Density ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Absorption Lines ◽  
Gravitational Lenses ◽  
High Column

A wealth of observational data supports the commonly held view that damped Lyman-α (Lyα) absorption in QSO spectra is associated with neutral-hydrogen (HI) disks in spiral galaxies. Most of the HI probed by QSO absorption lines is traced by damped Lyα lines because of their high column densities, N > 1020 cm–2. The spiral galaxies hosting the HI disks can act as gravitational lenses on the QSOs. If the HI column density increases towards the center of the disks, as suggested by observations of local galaxies, the magnification bias preferentially selects for high column-density systems. The estimates of HI in damped Lyα systems can then systematically be distorted by gravitational lensing.

scholarly journals Chemical Evolution of Spiral Galaxies from Redshift 4 to the Present

2002 ◽  
Vol 187 ◽  
pp. 147-151
Author(s):  
U. Fritze - v. Alvensleben ◽  
U. Lindner ◽  
K. J. Fricke
Keyword(s):  
High Resolution ◽  
Column Density ◽  
Spiral Galaxies ◽  
Narrow Range ◽  
High Resolution Spectroscopy ◽  
Early Type ◽  
Absorption Properties ◽  
Hii Region ◽  
The Galaxy ◽  
Ism Abundances

ISM abundances in nearby spiral galaxies are well known from HII region studies (Zaritsky et al. 1994). While early type spirals, Sa, Sb, have rather uniform abundances and a narrow range of present star formation rates (SFR) the galaxy-to-galaxy variations both in HII region abundances and in present SFR increase towards late spiral types Sc, Sd (see e.g. Kennicutt & Kent 1983). ISM abundances of spiral galaxies or their progenitors up to the highest redshifts can be studied via the absorption properties imprinted in the spectra of background QSOs. While MgII- and CIV- absorption lines are produced in the low column density gas of the extended haloes around galaxies, the Damped Lyα Absorption (DLA) is believed to originate in (proto-)galactic disks. High resolution spectroscopy of a large number of metal lines associated with DLA systems reveal the redshift evolution of ISM abundances from z ≳ 4 to z ~ 0.6.

scholarly journals The evolution of neutral hydrogen over the past 11 Gyr via H i 21 cm absorption

2020 ◽  
Vol 498 (1) ◽  
pp. 883-898 ◽  
Author(s):  
Kathryn Grasha ◽  
Jeremy Darling ◽  
Adam K Leroy ◽  
Alberto D Bolatto
Keyword(s):  
Mass Density ◽  
Neutral Hydrogen ◽  
Radio Frequency Interference ◽  
Spin Temperature ◽  
The Past ◽  
Neutral Gas ◽  
A Value ◽  
The Mean ◽  
Blind Search ◽  
Green Bank Telescope

ABSTRACT We present the results of a blind search for intervening H i 21 cm absorption towards 260 radio sources in the redshift range 0 < z < 2.74 with the Green Bank Telescope. The survey has the sensitivity to detect sub-damped Ly α (DLA) systems for H i spin temperatures Ts/f = 100 K, and despite the successful re-detection of 10 known 21 cm absorbers in the sample, we detect no new absorption lines in the full survey. Sources detected in 21 cm absorption were also searched for hydroxyl (OH) 18 cm absorption and we re-detect 1667 MHz OH absorption towards PKS 1830-211. We searched for intervening H i 21 cm absorption along the line of sight in each source achieving a total redshift coverage of Δz = 88.64 (comoving absorption path of ΔX = 159.5) after removing regions affected by radio frequency interference. We compute a 95 per cent confidence upper limit on the column density frequency distribution f(NH i) and set a statistical constraint on the spin temperature Ts in the range 100–1000 K, consistent with prior redshifted optical DLA surveys and H i 21 cm emission observations at the same redshifts. We infer a value for the cosmological mass density of neutral gas, ΩH i. Through comparison with prior ΩH i measurements, we place a statistical constraint on the mean spin temperature of Ts/f = 175 K. Our derived ΩH i values support a relative mild evolution in ΩH i over the last 11 Gyr and are consistent with other methods that measure ΩH i.

scholarly journals High-resolution 21-cm observations of low-column density gas clumps in the Milky Way halo

2009 ◽  
Vol 503 (2) ◽  
pp. 483-493 ◽  
Author(s):  
N. Ben Bekhti ◽  
P. Richter ◽  
B. Winkel ◽  
F. Kenn ◽  
T. Westmeier
Keyword(s):  
High Resolution ◽  
Column Density ◽  
Milky Way ◽  
Milky Way Halo

scholarly journals Analytic solutions to the maximum and average exoplanet transit depth for common stellar limb darkening laws

2019 ◽  
Vol 623 ◽  
pp. A137 ◽  
Author(s):  
René Heller
Keyword(s):  
Light Curve ◽  
Impact Parameter ◽  
Extrasolar Planets ◽  
Analytic Solutions ◽  
Radius Ratio ◽  
Average Intensity ◽  
The Mean ◽  
Impact Parameters ◽  
In Transit ◽  
Limb Darkening

Context. The depth of an exoplanetary transit in the light curve of a distant star is commonly approximated as the squared planet-to-star radius ratio, (Rp/Rs)2. Stellar limb darkening, however, can result in significantly deeper transits. An analytic solution would be worthwhile to illustrate the principles of the problem and predict the actual transit signal required for the planning of transit observations with certain signal-to-noise requirements without the need of computer-based transit simulations. Aims. We calculate the overshoot of the mid-transit depth caused by stellar limb darkening compared to the (Rp/Rs)2 estimate for arbitrary transit impact parameters. In turn, this allows us to compute the true planet-to-star radius ratio from the transit depth for a given parameterization of a limb darkening law and for a known transit impact parameter. Methods. We compute the maximum emerging specific stellar intensity covered by the planet in transit and derive analytic solutions for the transit depth overshoot. Solutions are presented for the linear, quadratic, square-root, logarithmic, and nonlinear stellar limb darkening with arbitrary transit impact parameters. We also derive formulae to calculate the average intensity along the transit chord, which allows us to estimate the actual transit depth (and therefore Rp∕Rs) from the mean in-transit flux. Results. The transit depth overshoot of exoplanets compared to the (Rp/Rs)2 estimate increases from about 15% for main-sequence stars of spectral type A to roughly 20% for sun-like stars and some 30% for K and M stars. The error in our analytical solutions for Rp∕Rs from the small planet approximation is orders of magnitude smaller than the uncertainties arising from typical noise in real light curves and from the uncertain limb darkening. Conclusions. Our equations can be used to predict with high accuracy the expected transit depth of extrasolar planets. The actual planet radius can be calculated from the measured transit depth or from the mean in-transit flux if the stellar limb darkening can be properly parameterized and if the transit impact parameter is known. Light curve fitting is not required.

scholarly journals High–Resolution V–Band Photometry of the Milky Way

1990 ◽  
Vol 139 ◽  
pp. 203-204
Author(s):  
B. Hoffmann ◽  
S. Kimeswenger ◽  
W. Schlosser ◽  
Th. Schmidt-Kaler ◽  
K. J. Seidensticker
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Brightness Distribution ◽  
Mean Deviation ◽  
Spherical Mirror ◽  
Image Size ◽  
V Band ◽  
Scan Time ◽  
The Mean ◽  
Wide Angle Camera

High resolution (0.°25 × 0.°25) surface brightness distribution in V of the southern Milky Way over an area of 200° ≤ l ≤ 60° and of −30° ≤ b ≤ +30° was obtained by photographic plates, taken at La Silla, Chile, with the super-wide-angle camera with spherical mirror of the Astronomisches Institut der Ruhr-Universität Bochum (Schmidt-Kaler et al. 1983). Schmidt-Kaler et al. (1983) and Seidensticker, Schmidt-Kaler, and Schlosser (1982) carried out an analysis of these plates. However, these studies used only a fraction of the whole plate; interesting parts of the sky were chosen near the plate centers, thus minimizing various errors. The plates are now all scanned over the whole field of view with a PDS with a diaphragm of 50 × 50 μm = 0.°12 × 0.° 12 on the sky. The image size is 1201 × 1201 pixels per plate. The mean deviation during the scan time was less than 0.1%. Through the identification of about 50 stars and by using their l, b and x, y coordinates, the equations of the plates were solved with eight geometric parameters. The standard deviation of all parameters was less than 0.3 pixels on all plates.

scholarly journals New Conversion Laws for CO Observations

2016 ◽  
Vol 11 (S321) ◽  
pp. 270-271
Author(s):  
Peter J. Barnes ◽  
Erik Muller ◽  
Audra K. Hernandez ◽  
Ana Duarte-Cabral ◽  
Frederic Schuller
Keyword(s):  
Molecular Mass ◽  
Column Density ◽  
Scaling Laws ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Galactic Plane ◽  
Large Fraction ◽  
Molecular Line ◽  
Physically Based ◽  
Co Observations

AbstractWe describe new conversion laws, from CO molecular line data to inferred mass column, based on observations of the three main CO isotopologues in several surveys of the Galactic Plane. The new conversion laws replace the use of the single “X-factor” in widespread use, with a more physically-based relationship between the CO line’s optical depth, excitation, and column density. It has the effect of increasing the inferred mass column, over the single X-factor, by typically a factor of 2–3. This means that the molecular mass of the Milky Way may have been substantially underestimated in previous studies, and suggests that scaling laws like the Kennicutt-Schmidt relations may also need to be recalibrated. Because of its statistical basis on a large fraction of our Galaxy’s ISM, this new law is also recommended for use in studies of other Milky-Way-analogue spiral galaxies.

scholarly journals Stellar metallicity variations across spiral arms in disk galaxies with multiple populations

2018 ◽  
Vol 611 ◽  
pp. L2 ◽  
Author(s):  
S. Khoperskov ◽  
P. Di Matteo ◽  
M. Haywood ◽  
F. Combes
Keyword(s):  
High Resolution ◽  
Spiral Galaxy ◽  
Spiral Galaxies ◽  
Stellar Populations ◽  
Disk Galaxies ◽  
Model Composite ◽  
Spiral Arms ◽  
Radial Migration ◽  
The Mean ◽  
Spiral Arm

This Letter studies the formation of azimuthal metallicity variations in the disks of spiral galaxies in the absence of initial radial metallicity gradients. Using high-resolution N-body simulations, we model composite stellar discs, made of kinematically cold and hot stellar populations, and study their response to spiral arm perturbations. We find that, as expected, disk populations with different kinematics respond differently to a spiral perturbation, with the tendency for dynamically cooler populations to show a larger fractional contribution to spiral arms than dynamically hotter populations. By assuming a relation between kinematics and metallicity, namely the hotter the population, the more metal-poor it is, this differential response to the spiral arm perturbations naturally leads to azimuthal variations in the mean metallicity of stars in the simulated disk. Thus, azimuthal variations in the mean metallicity of stars across a spiral galaxy are not necessarily a consequence of the reshaping, by radial migration, of an initial radial metallicity gradient. They indeed arise naturally also in stellar disks which have initially only a negative vertical metallicity gradient.

scholarly journals H i column density statistics of the cold neutral medium from absorption studies

2019 ◽  
Author(s):  
Pavan Kumar Vishwakarma ◽  
Prasun Dutta
Keyword(s):  
Thermal Properties ◽  
Column Density ◽  
Neutral Hydrogen ◽  
Density Fluctuations ◽  
Neutral Medium ◽  
Spin Temperature ◽  
Scale Invariant ◽  
Absorption Studies ◽  
Scale Structures ◽  
Invariant Properties

Abstract Physical properties of the tiny scale structures in the cold neutral medium (CNM) of galaxies is a long-standing puzzle. Only a few lines of sights in our Galaxy have been studies with mixed results on the scale-invariant properties of such structures. Moreover, since these studies measure the variation of neutral hydrogen optical depth, they do not directly constrain the density structures. In this letter, we investigate the possibility of measuring the properties of density and spin temperature structures of the H i from absorption studies of H i . Our calculations show that irrespective of the thermal properties of the clouds, the scale structure of the H i column density can be estimated, whereas, H i absorption studies alone cannot shed much light on either the amplitude of the density fluctuations and their temperature structures. Detailed methodology and calculations with some fiducial examples are presented.

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

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