arXiv subjects

A. M. Wolfe

Publications and source records attributed to A. M. Wolfe.

14 recordsLinked to original sources

arXiv2012

The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium

By comparing the widths of absorption lines from OI, SiII and FeII in the redshift z=2.076 single-component damped Lyman alpha absorption system in the spectrum of Q2206-199 we establish that these absorption lines arise in Warm Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies, but not with the presence of a significant cold component. It is also consistent with, but not required by, the absence of CII* fine structure absorption in this system. Some possible implications concerning abundance estimates in narrow-line WNM absorbers are discussed.

astro-ph.GA↗

arXiv2011

The Transitional Stripped-Envelope SN 2008ax: Spectral Evolution and Evidence for Large Asphericity

Supernova (SN) 2008ax in NGC 4490 was discovered within hours after shock breakout, presenting the rare opportunity to study a core-collapse SN beginning with the initial envelope-cooling phase immediately following shock breakout. We present an extensive sequence of optical and near-infrared spectra, as well as three epochs of optical spectropolarimetry. Our initial spectra, taken two days after shock breakout, are dominated by hydrogen Balmer lines at high velocity. However, by maximum light, He I lines dominated the optical and near-infrared spectra, which closely resembled those of normal Type Ib supernovae (SNe Ib) such as SN 1999ex. This spectroscopic transition defines Type IIb supernovae, but the strong similarity of SN 2008ax to normal SNe Ib beginning near maximum light, including an absorption feature near 6270A due to H-alpha at high velocities, suggests that many objects classified as SNe Ib in the literature may have ejected similar amounts of hydrogen as SN 2008ax, roughly a few x 0.01 M_sun. Early-time spectropolarimetry (6 and 9 days after shock breakout) revealed strong line polarization modulations of 3.4% across H-alpha, indicating the presence of large asphericities in the outer ejecta. The continuum shares a common polarization angle with the hydrogen, helium, and oxygen lines, while the calcium and iron absorptions are oriented at different angles. This is clear evidence of deviations from axisymmetry even in the outer ejecta. Intrinsic continuum polarization of 0.64% only nine days after shock breakout shows that the outer layers of the ejecta were quite aspherical. A single epoch of late-time spectropolarimetry, as well as the shapes of the nebular line profiles, demonstrate that asphericities extended from the outermost layers all the way down to the center of this SN. [Abridged]

astro-ph.SR↗

arXiv2010

Cosmological concordance or chemical coincidence? Deuterated molecular hydrogen abundances at high redshift

We report two detections of deuterated molecular hydrogen (HD) in QSO absorption-line systems at $z > 2$. Toward J2123-0500, we find $N$(HD) $= 13.84 \pm 0.2$ for a sub-DLA with metallicity $\simeq 0.5Z_{\odot}$ and $N$(H$_2$) = $17.64 \pm 0.15$ at $z = 2.0594$. Toward FJ0812+32, we find $N$(HD) $= 15.38 \pm 0.3$ for a solar-metallicity DLA with $N$(H$_2$) = $19.88 \pm 0.2$ at $z = 2.6265$. These systems have ratios of HD to H$_2$ above that observed in dense clouds within the Milky Way disk and apparently consistent with a simple conversion from the cosmological ratio of D/H. These ratios are not readily explained by any available model of HD chemistry and there are no obvious trends with metallicity or molecular content. Taken together, these two systems and the two published $z > 2$ HD-bearing DLAs indicate that HD is either less effectively dissociated or more efficiently produced in high-redshift interstellar gas, even at low molecular fraction and/or solar metallicity. It is puzzling that such diverse systems should show such consistent HD/H$_2$ ratios. Without clear knowledge of all the aspects of HD chemistry that may help determine the ratio HD/H$_2$, we conclude that these systems are potentially more revealing of gas chemistry than of D/H itself and that it is premature to use such systems to constrain D/H at high-redshift.

astro-ph.CO↗

arXiv2009

The Quasar SDSS J1536+0441: An Unusual Double-Peaked Emitter

The quasar SDSS J153636.22+044127.0, exhibiting peculiar broad emission-line profiles with multiple components, was proposed as a candidate sub-parsec binary supermassive black hole system. More recently, imaging revealed two spatially distinct sources, leading some to suggest the system to be a quasar pair separated by ~5 kpc. We present Palomar and Keck optical spectra of this system from which we identify a third velocity component to the emission lines. We argue that the system is more likely an unusual member of the class of active galactic nuclei (AGNs) known as "double-peaked emitters" than a sub-parsec black hole binary or quasar pair. We find no significant velocity evolution of the two main peaks over the course of 0.95 yr, with a 3-sigma upper limit on any secular change of 70 km/s/yr. We also find that the three velocity components of the emission lines are spatially coincident to within 0.015" along the slit, apparently ruling out the double-quasar hypothesis.

astro-ph.CO↗

arXiv2008

Probing feedback in protogalaxies: Multiphase gas in a DLA at z~2.4

We investigate the physical processes occuring in the multiphase gas of a damped Lyαsystem (DLA). We base our analysis on a high quality Keck HIRES spectrum of the QSO J1211+0422 in which a DLA is detected at z=2.377. There is little contamination of the high-ion (OVI, NV, CIV, SiIV) absorption, allowing us to explore the properties of the highly ionized gas and its connection to other gas-phases. The metallicity ([Z/H]=-1.41+/-0.08), HI column density (log N(HI)=20.80+/-0.10), full-width velocity (Δ(v_ neut)=70 km/s) and relative abundances ([Si/Fe]=+0.23+/-0.05 and [N/Si]=-0.88+/-0.07) of this DLA are not unusual. However, we derive the lowest CII* cooling rate in a DLA, l_c < 10^{-27.8} erg/s per H atom (3σ). Using this stringent limit, we show that the neutral gas (confined at |v|<+39 km/s) must be warm and the star formation rate is <7.1x10^{-3} M_odot/yr/kpc^2. Surprisingly, the gas shows strong, complex absorption profiles from highly ionized gas whose kinematics appear connected to each other and the low ions. The total amount of highly and weakly ionized gas is very large with N(HII)/N(HI)>1.5. At |v|>+39 km/s, the gas is fully and highly ionized (H+/H~1, N(CIV)>>N(CII), N(SiIV)>>N(SiII)). Based on ionization models, OVI and NV are generally difficult to produce by hard photons, while SiIV and CIV can be photoionized to a large extent. There is, however, no evidence of OVI-bearing gas at T~10^6 K associated with this DLA. In contrast, there is some evidence for narrow OVI, NV, and CIV components (unexplained by photoionization), implying too low temperatures (T < 10^5 K) for simple collisional ionization models to produce their observed column densities. Stellar feedback is a possible source for producing the high ions, but we cannot rule out accretion of non-pristine material onto the protogalaxy.

astro-ph↗

arXiv2005

Measurement of the Spatial Cross-Correlation Function of Damped Lyman Alpha Systems and Lyman Break Galaxies

We present the first spectroscopic measurement of the spatial cross-correlation function between damped Lyman alpha systems (DLAs) and Lyman break galaxies (LBGs). We obtained deep u'BVRI images of nine QSO fields with 11 known z ~ 3 DLAs and spectroscopically confirmed 211 R < 25.5 photometrically selected z > 2 LBGs. We find strong evidence for an overdensity of LBGs near DLAs versus random, the results of which are similar to that of LBGs near other LBGs. A maximum likelihood cross-correlation analysis found the best fit correlation length value of r_0 = 2.9^(+1.4)_(-1.5) h^(-1)Mpc using a fixed value of gamma = 1.6. The implications of the DLA-LBG clustering amplitude on the average dark matter halo mass of DLAs are discussed.

astro-ph↗

arXiv2004

Survey for Galaxies Associated with z~3 Damped Lyman alpha Systems I: Spectroscopic Calibration of u'BVRI Photometric Selection

We present a survey for z~3 Lyman break galaxies (LBGs) associated with damped Lyman alpha systems (DLAs) with the primary purpose of determining the DLA-LBG cross-correlation. This paper describes the acquisition and analysis of imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343 sources detected in the field. Spectroscopic observations of 529 LBG candidates using Keck LRIS yielded 339 redshifts. We have conservatively identified 211 z>2 objects with =3.02+/-0.32. We discuss our method of z~3 LBG identification and present a model of the u'BVRI photometric selection function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break photometric selection technique.

astro-ph↗

arXiv2003

Constraining Variations in the Fine-structure Constant, Quark Masses and the Strong Interaction

We present evidence for variations in the fine-structure constant from Keck/HIRES spectra of 143 quasar absorption systems over the redshift range 0.2 < z_abs < 4.2. This includes 15 new systems, mostly at high-z (z_abs > 1.8). Our most robust estimate is a weighted mean da/a=(-0.57 +/- 0.11)x10^{-5}. We respond to recent criticisms of the many-multiplet method used to extract these constraints. The most important potential systematic error at low-z is the possibility of very different Mg heavy isotope abundances in the absorption clouds and laboratory: {\it higher} abundances of {25,26}Mg in the absorbers may explain the low-z results. Approximately equal mixes of {24}Mg and {25,26}Mg are required. Observations of Galactic stars generally show {\it lower} {25,26}Mg isotope fractions at the low metallicities typifying the absorbers. Higher values can be achieved with an enhanced population of intermediate mass stars at high redshift, a possibility at odds with observed absorption system element abundances. At present, all observational evidence is consistent with the varying-alpha results. Another promising method to search for variation of fundamental constants involves comparing different atomic clocks. Here we calculate the dependence of nuclear magnetic moments on quark masses and obtain limits on the variation of alpha and m_q/Lambda_QCD from recent atomic clock experiments with hyperfine transitions in H, Rb, Cs, Hg+ and an optical transition in Hg+.

astro-ph↗

arXiv2002

Metal abundances and kinematics of quasar absorbers - II. Absorption systems toward Q0347-3819 and APM BR J0307-4945

Detailed Monte Carlo Inversion analysis of the spectral lines from three Lyman limit systems (LLS) [N(HI) > 10^{17} cm^-2] and nine lower N(HI) systems [2 10^{14} < N(HI) < 2 10^{16} cm^-2] observed in the VLT/UVES spectra of Q0347-3819 (in the range 2.21 <= z <= 3.14) and of APM BR J0307-4945 (at z = 4.21 and 4.81) is presented. Combined with the results from a previous work, the analyzed LLSs show that they are a heterogeneous population originating in different environments. A functional dependence of the line-of-sight velocity dispersion sigma_v on the absorber size L is confirmed: the majority of the analyzed systems follow the scaling relation sigma_v ~ (N_H L)^{0.3} (with N_H being the total gas column density). This means that most absorbers may be related to virialized systems like galaxies or their halos. Previously noted enhancement of the metal content in small size systems is also confirmed: metallicities of Z ~ (1/3-1/2)Z_solar are found in systems with L < 0.4 kpc, whereas we observe much lower metal abundances in systems with larger linear sizes. For the first time in LLSs, a pronounced [alpha-element/iron-peak] enrichment is revealed: the absorber at z = 2.21 shows [O/Fe] = 0.65+/-0.11, [Si/Fe] = 0.51+/-0.11, and [Mg/Fe] = 0.38+/-0.11. Several absorption systems exhibit characteristics which are very similar to that observed in high-velocity clouds in the Milky Way and may be considered as high-redshift counterparts of Galactic HVCs.

astro-ph↗

arXiv2001

Possible evidence for a variable fine structure constant from QSO absorption lines: motivations, analysis and results

An experimental search for variation in the fundamental coupling constants is strongly motivated by modern high-energy physics theories. Comparison of quasar absorption line spectra with laboratory spectra provides a sensitive probe for variability of the fine structure constant, alpha, over cosmological time-scales. We have previously developed and applied a new method providing an order of magnitude gain in precision over previous optical astrophysical constraints. Here we extend that work by including new quasar spectra of damped Lyman-alpha absorption systems. We also re-analyse our previous lower redshift data and confirm our initial results. The constraints on alpha come from simultaneous fitting of absorption lines of subsets of the following species: Mg I, Mg II, Al II, Al III, Si II, Cr II, Fe II, Ni II and Zn II. We present a detailed description of our methods and results based on an analysis of 49 quasar absorption systems (towards 28 QSOs) covering the redshift range 0.5 < z < 3.5. There is statistical evidence for a smaller alpha at earlier epochs: da/a = (-0.72 +/- 0.18) * 10^{-5}. The new and original samples are independent but separately yield consistent and significant non-zero values of da/a. We summarise the results of a thorough investigation of systematic effects published in a companion paper. The value we quote above is the raw value, not corrected for any of these systematic effects. The only significant systematic effects so far identified, if removed from our data, would lead to a more significant deviation of da/a from zero.

astro-ph↗

arXiv2001

Further Evidence for Cosmological Evolution of the Fine Structure Constant

We describe the results of a search for time variability of the fine structure constant, alpha, using absorption systems in the spectra of distant quasars. Three large optical datasets and two 21cm/mm absorption systems provide four independent samples, spanning 23% to 87% of the age of the universe. Each sample yields a smaller alpha in the past and the optical sample shows a 4-sigma deviation: da/a = -0.72 +/- 0.18 x 10^{-5} over the redshift range 0.5 < z < 3.5. We find no systematic effects which can explain our results. The only potentially significant systematic effects push da/a towards positive values, i.e. our results would become more significant were we to correct for them.

astro-ph↗

arXiv2001

Further constraints on variation of the fine structure constant from alkali doublet QSO absorption lines

Comparison of quasar absorption line spectra with laboratory spectra provides a precise probe for variability of the fine structure constant, alpha, over cosmological time-scales. We constrain variation in alpha in 21 Keck/HIRES Si IV absorption systems using the alkali doublet (AD) method in which changes in alpha are related to changes in the doublet spacing. The precision obtained with the AD method has been increased by a factor of 3: da/a = (-0.5 +/- 1.3) * 10^{-5}. We also analyse potential systematic errors in this result. Finally, we compare the AD method with the many-multiplet method which has achieved an order of magnitude greater precision and we discuss the future of the AD method.

astro-ph↗

arXiv1997

Warm Neutral Gas at Redshift 3.4

Radio spectroscopy at 323 MHz using the Arecibo Telescope and the VLA has produced a tentative detection of the 21cm line of neutral hydrogen at Z_abs=3.38716+-0.00007 in absorption against the radio continuum of the QSO MG0201+113 (Z_em = 3.61). This redshift roughly agrees with one determined by the Westerbork Synthesis Radio Telescope and reported earlier; however the observations at different telescopes produce different results for width and optical depth of the line. If the detection holds, it provides evidence for a high column density of neutral gas that is confined to a dynamically cold layer with velocity dispersion ~10 km/s. Although the interpretation is uncertain due to a lack of detailed knowledge of the extended radio structure of the background quasar and the relative quantities of neutral gas in the cold and turbulent components, the observations specify high spin temperatures, T_s > 1000 K for both this 21cm line absorbing cloud and the turbulent component, which together have N_HI ~ 10^21.4 cm^-2. Results of optical spectroscopy require the additional presence of metal-enriched clouds of still broader velocity dispersion than the 21cm line, creating a picture which is consistent with this system being a young disk galaxy that is sufficiently evolved by z=3.4 to have collapsed to a flattened system and produced a population of stars that have aged to pollute a turbulent halo. The observations constrain the neutral gas mass of a possible 21cm line emitter associated with the intervening absorber to be less than ~(Delta V/200 km/s) 10^13 Msolar for velocity widths Delta V (FWHM) in the range 200 to 1200 km/s (H_o=100 km/s/Mpc, Omega_o=1).

astro-ph↗

arXiv1996

The HST Quasar Absorption Line Key Project XII. The Unusual Absorption Line System in the Spectrum of PG 2302+029 ---Ejected or Intervening?

We report the discovery of a high-ionization broad absorption line system at a redshift of z_abs=0.695 in the spectrum of the z_em=1.052 radio-quiet quasar PG 2302+039. Broad absorption with FWHM from 3,000 to 5,000 km/s is detected from C IV, N V, and O VI in HST Faint Object Spectrograph spectra of the quasar. A narrow line system (FWHM approximately 250 km/s) at z_abs=0.7016 is resolved from the broad blend and includes absorption by Ly-alpha and the C IV, N V, and O VI doublets. No absorption by low-ionization metal species (e.g. Si II and Mg II) is detected in the HST or ground-based spectra for either the broad or the narrow system. The centroids of the broad system lines are displaced by approximately 56,000 km/s to the blue of the quasar's broad emission lines. The reddest extent of the broad line absorption is more than 50,000 km/s from the quasar. The properties of this system are unprecedented whether it is an intervening or an ejected system.

astro-ph↗