arXiv subjects

Bart Wakker

Publications and source records attributed to Bart Wakker.

10 recordsLinked to original sources

arXiv2026

Circumgalactic CIV Absorption Found Only Within 30 Degrees of the Minor Axis of Present-Epoch Galaxies

We studied CIV 1548,1550 absorption in the circumgalactic medium (CGM) of 88 isolated, bright (L_B > 0.2L*_B) galaxies at z < 0.03 selected without prior knowledge of CGM absorption. The galaxies have observationally-unbiased distributions of inclination and galaxy-quasar sightline azimuthal angle. Above a 5-sigma rest-frame equivalent width detection threshold of W_r > 0.1 angstroms, we found absorption in the CGM of 9/88 of the galaxies within projected separation R_perp < 350 kpc. All nine absorbers arise within 30 deg of the projected minor axes and R_perp < 1.2R_vir of star-forming galaxies [log(sSFR/yr^-1) > -10.75]. To a confidence level of 99.998% (4.3-sigma), we can rule out that these absorbers are drawn from a random distribution of galaxy-quasar azimuthal angles. These findings suggest strong evidence for biconical polar winds related to the moderately elevated star formation in these present-epoch galaxies and we describe simple spatial-kinematic models that support this hypothesis. High specific star-formation rates may not be a sufficient condition for predicting minor-axis CIV absorption because the covering fraction of the subsample of star-forming galaxies within 30 deg of their minor axes is f_cov ~ 0.5; this may imply transient and/or patchy outflows. Incorporating studies of MgII and OVI CGM absorption, we favor a scenario in which CIV-bearing CGM gas interfaces between these low- and high-ionization regimes, comprising enriched intermediate-ionization clouds entrained and collimated in biconical stellar winds while mixing and cooling via non-equilibrium photoionization.

astro-ph.GA↗

arXiv2026

High-S/N Quasar Observations with HST/COS: Deep Fields for Spectroscopy

Hubble is still in prime observing condition for making transformative discoveries in UV astronomy. In this white paper we describe the science case for a deep (S/N>30) UV spectroscopic survey with HST/COS targeting approximately 20 QSOs at 0.5<z<1.5 at good resolution (20 km/s). This survey would capitalize on our current UV capability, produce a legacy dataset enabling community science in many areas of galactic and extragalactic research, and pioneer a path for future UV science with the Habitable Worlds Observatory. Such high-S/N spectra are largely missing from the MAST archives, and would be analogous to the deep Hubble imaging fields (HDF, UDF, Frontier Fields) that have been enormously successful and far-reaching in their science impact. This legacy dataset would enable frontier science programs in several areas, including (1) studies of the CGM and IGM at unparalleled sensitivity, covering a wide range of UV metal lines and reaching very low H I column densities of log N=12.6 and low metallicities near [Z/H]=-2, enabling precision studies of the chemical abundances, ionization, temperature, and baryon and metal budgets of the CGM and IGM; (2) diffuse gas in the Milky Way and Local Group, including high-velocity clouds and gas streams from satellite mergers; (3) AGN outflows, which would be probed in the rest-frame extreme ultraviolet (EUV), covering continuum-generation mechanisms and diagnostics of gas in accretion-disk outflows.

astro-ph.GA↗

arXiv2025

Dust in the Smith Cloud? A UV Investigation into the Smith Cloud's Gas-Phase Abundance Patterns

The Smith Cloud is a high-velocity cloud (HVC) on its final approach to the Milky Way that shows evidence of interaction with the Galaxy's disk. We investigate the metallicity and gas-phase chemical depletion patterns in this HVC using UV absorption-line observations toward two background QSOs taken with the Hubble Space Telescope (HST)/Cosmic Origin Spectrograph (COS) and H I 21-cm emission-line observations taken with Green Bank Telescope (GBT). We find evidence of silicon gas-phase depletion with [Si/S]$=\,-0.72^{+0.26}_{-0.24}$ and [Si/O]$_{3σ}\,\lesssim\,-0.05$, implying the presence of dust within the Smith Cloud. Because dust is galactic in origin, this HVC could trace the return leg of a Galactic fountain or a dwarf galaxy that passed through the Galactic plane.

astro-ph.GA↗

arXiv2022

Probing the physicochemical properties of the Leo Ring and the Leo I group

We present an absorption line study of the physical and chemical properties of the Leo HI Ring and the Leo I Group as traced by 11 quasar sightlines spread over a 600 kpc X 800 kpc region. Using HST/COS G130/G160 archival observations as constraints, we couple cloud-by-cloud, multiphase, Bayesian ionization modeling with galaxy property information to determine the plausible origin of the absorbing gas along these sightlines. We search for absorption in the range 600 km/s - 1400 km/s consistent with the kinematics of the Leo Ring/Group. We find absorption plausibly associated with the Leo Ring towards five sightlines. Along three other sightlines, we find absorption likely to be associated with individual galaxies, intragroup gas, and/or large-scale filamentary structure. The absorption along these five sightlines is stronger in metal lines than expected from individual galaxies, indicative of multiple contributions, and of the complex kinematics of the region. We also identify three sightlines within a 7-degree X 6-degree field around the Leo Ring, along which we do not find any absorption. We find that the metallicities associated with the Leo Ring are generally high, with values between solar and several times solar. The inferred high metallicities are consistent with the origin of the ring as tidal debris from a major galaxy merger.

astro-ph.GA↗

arXiv2015

Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy

We demonstrate the presence of an extended and massive circumgalactic medium (CGM) around Messier 31 using archival HST COS ultraviolet spectroscopy of 18 QSOs projected within two virial radii of M31 (Rvir=300 kpc). We detect absorption from SiIII at -300 Rvir. We show that the M31 CGM gas is bound, multiphase, predominantly ionized (i.e., HII>>HI), and becomes more highly ionized gas at larger R. We estimate using SiII, SiIII, and SiIV a CGM metal mass of at least 2x10^6 Msun and gas mass of >3x10^9(Zsun/Z) Msun within 0.2 Rvir, and possibly a factor ~10 larger within Rvir, implying substantial metal and gas masses in the CGM of M31. Compared with galaxies in the COS-Halos survey, the CGM of M31 appears to be quite typical for a L* galaxy.

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arXiv2012

Unique Astrophysics in the Lyman Ultraviolet

There is unique and groundbreaking science to be done with a new generation of UV spectrographs that cover wavelengths in the "Lyman Ultraviolet" (LUV; 912 - 1216 Ang). There is no astrophysical basis for truncating spectroscopic wavelength coverage anywhere between the atmospheric cutoff (3100 Ang) and the Lyman limit (912 Ang); the usual reasons this happens are all technical. The unique science available in the LUV includes critical problems in astrophysics ranging from the habitability of exoplanets to the reionization of the IGM. Crucially, the local Universe (z <= 0.1) is entirely closed to many key physical diagnostics without access to the LUV. These compelling scientific problems require overcoming these technical barriers so that future UV spectrographs can extend coverage to the Lyman limit at 912 Ang.

astro-ph.IM↗

arXiv2009

Significant foreground unrelated non-acoustic anisotropy on the one degree scale in WMAP 5-year observations

The spectral variation of the cosmic microwave background (CMB) as observed by WMAP was tested using foreground reduced WMAP5 data, by producing subtraction maps at the 1$^\circ$ angular resolution between the two cosmological bands of V and W, for masked sky areas that avoid the Galactic disk. The resulting $V-W$ map revealed a non-acoustic signal over and above the WMAP5 pixel noise, with two main properties. Firstly, it possesses quadrupole power at the $\approx$ 1 $μK$ level which may be attributed to foreground residuals. Second, it fluctuates also at all values of $\ell >$ 2, especially on the $1^\circ$ scale ($200 \lesssim \ell \lesssim 300$). The behavior is {\it random and symmetrical} about zero temperature with a r.m.s. amplitude of $\approx$ 7 $μK$, or 10 % of the maximum CMB anisotropy, which would require a `cosmic conspiracy' among the foreground components if it is a consequence of their existences. Both anomalies must be properly diagnosed and corrected if `precision cosmology' is the claim. The second anomaly is, however, more interesting because it opens the question on whether the CMB anisotropy genuinely represents primordial density seeds.

astro-ph.CO↗

arXiv2009

The Extension of the Transition Temperature Plasma into the Lower Galactic Halo

Column densities for H I, Al III, Si IV, C IV, and O VI toward 109 stars and 30 extragalactic objects have been assembled to study the extensions of these species away from the Galactic plane into the Galactic halo. H I and Al III mostly trace the warm neutral and warm ionized medium, respectively, while Si IV, C IV and O VI trace a combination of warm photoionized and collisionally ionized plasmas. The much larger object sample compared to previous studies allows us to consider and correct for the effects of the sample bias that has affected earlier but smaller surveys of the gas distributions. We find Si IV and C IV have similar exponential scale heights of 3.2(+1.0, -0.6) and 3.6(+1.0, -0.8) kpc. The scale height of O VI is marginally smaller with h = 2.6+/- 0.6 kpc. The transition temperature gas is ~3 times more extended than the warm ionized medium traced by Al III with h = 0.90(+0.62, -0.33) kpc and ~12 times more extended than the warm neutral medium traced by H I with h = 0.24 +/- 0.06 kpc. There is a factor of 2 decrease in the dispersion of the log of the column density ratios for transition temperature gas for lines of sight in the Galactic disk compared to extragalactic lines of sight through the entire halo. The observations are compared to the predictions of the various models for the production of the transition temperature gas in the halo. The appendix presents a revision to the electron scale height proposed by Gaensler et al. (2008) based on electron dispersion measures.

astro-ph.GA↗

arXiv2007

The Abundance of Deuterium in the Warm Neutral Medium of the Lower Galactic Halo

We use high resolution spectra obtained with FUSE and STIS to obtain interstellar column densities of H I, D I, O I, S II, Fe II and P II toward the QSO HE 0226-4110 ( l = 253.4 deg , b = -65.77 deg). We obtain D/H = 21(+8, -6) ppm. Correcting for a small amount of contamination from D and H in the Local Bubble, we obtain D/H = 22 (+8, -6) for the warm neutral medium of the lower Galactic halo. The medium has [O/H] = 0.12(+0.41, -0.20) and [Fe/H] = -1.01 (+0.10, -0.09). This suggests the abundances in the halo toward HE 0226-4110 are not affected by the infall of low metallicity gas and that the gas originates in the disk and is elevated into the halo by energetic processes which erode but do not totally destroy the dust grains. We compare our result to measured values of D/H in other astrophysical sites. The value we measure in the halo gas is consistent with the hypothesis that for many Galactic disk lines of sight D is incorporated into dust. The high average value of D/H = 23.1+/-2.4 ppm measured along 5 sight lines through disk gas in the Solar neighborhood is similar to D/H in the lower Galactic halo. These observations imply the abundance of deuterium in the Galaxy has only been reduced by a factor of 1.12+/-0.13 since its formation.

astro-ph↗

arXiv2003

Searching for the Intra-Group Medium in Loose Groups of Galaxies

We have conducted a study with the VLA, DRAO Synthesis Telscope, and the FUSE satellite to search for the intra-group medium in two loose groups of galaxies: GH 144 and GH 158. No HI was detected near the background AGN in GH 158, however two previously unknown dwarf galaxies were detected in GH 144. Lyman-alpha, -beta, CIII and NV absorption was detected in GH 144 by FUSE. Using this data and previously published data we found that the virial mass of GH 144 is 2x10^12 M(sun). Of this 8% lies in the individual group galaxies, and less than 8% is in the dense neutral intra-group medium. From our absorption line data we constrain the diffuse IGM to have a volume density greater than log n = -5.2 in a layer less than 22 kpc thick assuming a metallicity of 0.4 solar. While these values are uncertain, it is unlikely that this diffuse gas contributes a significant fraction of the group mass. Given the depth of the absorbing material and its separation from the nearest galaxies, it seems most likely it originates from a small-clump in the IGM, perhaps an ionized high-velocity cloud. (abridged)

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