We have used flux-transmission correlations in Lyα forests to measure the imprint of baryon acoustic oscillations (BAO). The study uses spectra of 157 783 quasars in the redshift range 2.1 ≤ z ≤ 3.5 ...from the Sloan Digital Sky Survey (SDSS) data release 12 (DR12). Besides the statistical improvements on our previous studies using SDSS DR9 and DR11, we have implemented numerous improvements in the analysis procedure, allowing us to construct a physical model of the correlation function and to investigate potential systematic errors in the determination of the BAO peak position. The Hubble distance, DH = c/H(z), relative to the sound horizon is DH(z = 2.33) /rd = 9.07 ± 0.31. The best-determined combination of comoving angular-diameter distance, DM, and the Hubble distance is found to be DH0.7DM0.3 /rd = 13.94 ± 0.35. This value is 1.028 ± 0.026 times the prediction of the flat-ΛCDM model consistent with the cosmic microwave background (CMB) anisotropy spectrum. The errors include marginalization over the effects of unidentified high-density absorption systems and fluctuations in ultraviolet ionizing radiation. Independently of the CMB measurements, the combination of our results and other BAO observations determine the open-ΛCDM density parameters to be ΩM = 0.296 ± 0.029, ΩΛ = 0.699 ± 0.100 and Ωk = −0.002 ± 0.119.
We present a measurement of baryon acoustic oscillations (BAO) in the cross-correlation of quasars with the Lyα-forest flux transmission at a mean redshift of z = 2.40. The measurement uses the ...complete Sloan Digital Sky Survey (SDSS-III) data sample: 168 889 forests and 234 367 quasars from the SDSS data release DR12. In addition to the statistical improvement on our previous study using DR11, we have implemented numerous improvements at the analysis level enabling a more accurate measurement of this cross-correlation. We have also developed the first simulations of the cross-correlation that allow us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the BAO peak position. We measure the two ratios DH(z = 2.40) /rd = 9.01 ± 0.36 and DM(z = 2.40) /rd = 35.7 ± 1.7, where the errors include marginalization over the non-linear velocity of quasars and the cross-correlation of metals and quasars, among other effects. These results are within 1.8σ of the prediction of the flat-ΛCDM model describing the observed cosmic microwave background anisotropies. We combine this study with the Lyα-forest auto-correlation function, yielding DH(z = 2.40) /rd = 8.94 ± 0.22 and DM(z = 2.40) /rd = 36.6 ± 1.2, within 2.3σ of the same flat-ΛCDM model.
Abstract
We report Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy of 10 quasars with foreground star-forming galaxies at 0.02 <
z
< 0.14 within impact parameters of ∼1–7 kpc. We ...detect damped/sub-damped Ly
α
(DLA/sub-DLA) absorption in 100% of cases where no higher-redshift Lyman-limit systems extinguish the flux at the expected wavelength of Ly
α
absorption, obtaining the largest targeted sample of DLA/sub-DLAs in low-redshift galaxies. We present absorption measurements of neutral hydrogen and metals. Additionally, we present Green Bank Telescope 21 cm emission measurements for five of the galaxies (including two detections). Combining our sample with the literature, we construct a sample of 117 galaxies associated with DLA/sub-DLAs spanning 0 <
z
< 4.4, and examine trends between gas and stellar properties, and with redshift. The H
i
column density is anticorrelated with impact parameter and stellar mass. More massive galaxies appear to have gas-rich regions out to larger distances. The specific star formation rate (sSFR) of absorbing galaxies increases with redshift and decreases with
M
*, consistent with evolution of the star formation main sequence (SFMS). However, ∼20% of absorbing galaxies lie below the SFMS, indicating that some DLA/sub-DLAs trace galaxies with longer-than-typical gas-depletion timescales. Most DLA/sub-DLA galaxies with 21 cm emission have higher H
i
masses than typical galaxies with comparable
M
*. High
M
HI
/
M
* ratios and high sSFRs in DLA/sub-DLA galaxies with
M
* < 10
9
M
⊙
suggest these galaxies may be gas-rich because of recent gas accretion rather than inefficient star formation. Our study demonstrates the power of absorption and emission studies of DLA/sub-DLA galaxies for extending galactic evolution studies to previously under-explored regimes of low
M
* and low SFR.
Abstract
We report the first direct measurement of the helium isotope ratio,
3
He/
4
He, outside of the Local Interstellar Cloud, as part of science-verification observations with the upgraded ...CRyogenic InfraRed Echelle Spectrograph. Our determination of
3
He/
4
He is based on metastable He
i
* absorption along the line of sight toward Θ
2
A Ori in the Orion Nebula. We measure a value
3
He/
4
He = (1.77 ± 0.13) × 10
−4
, which is just ∼40% above the primordial relative abundance of these isotopes, assuming the Standard Model of particle physics and cosmology, (
3
He/
4
He)
p
= (1.257 ± 0.017) × 10
−4
. We calculate a suite of galactic chemical evolution simulations to study the Galactic build up of these isotopes, using the yields from Limongi & Chieffi for stars in the mass range
M
= 8–100
M
⊙
and Lagarde et al. for
M
= 0.8–8
M
⊙
. We find that these simulations simultaneously reproduce the Orion and protosolar
3
He/
4
He values if the calculations are initialized with a primordial ratio
3
He
/
4
He
p
=
(
1.043
±
0.089
)
×
10
−
4
. Even though the quoted error does not include the model uncertainty, this determination agrees with the Standard Model value to within ∼2
σ
. We also use the present-day Galactic abundance of deuterium (D/H), helium (He/H), and
3
He/
4
He to infer an empirical limit on the primordial
3
He abundance,
3
He
/
H
p
≤
(
1.09
±
0.18
)
×
10
−
5
, which also agrees with the Standard Model value. We point out that it is becoming increasingly difficult to explain the discrepant primordial
7
Li/H abundance with nonstandard physics, without breaking the remarkable simultaneous agreement of three primordial element ratios (D/H,
4
He/H, and
3
He/
4
He) with the Standard Model values.
We present the study of a Lyman limit system (LLS) at zabs = 1.5441 toward quasar J134122.50+185213.9 observed with VLT X-shooter. This is a very peculiar system with strong C i absorption seen ...associated with a neutral hydrogen column density of log N(H i) (cm−2) = 18.10, too small to shield the gas from any external UV flux. The low-ionization absorption lines exhibit a simple kinematic structure consistent with a single component. Using CLOUDY models to correct for ionization, we find that the ionization parameter of the gas is in the range −4.5 < log U < -4.2 and the gas density -1.5 < log n(H) (cm−3) < -1.2. The models suggest that carbon is overabundant relative to iron, C/Fe > +2.2 at Fe/H ∼-1.6. Such a metal abundance pattern is reminiscent of carbon-enhanced metal-poor stars detected in the Galaxy halo. Metal enrichment by the first generation of supernovae provide a plausible explanation for the inferred abundance pattern in this system.
We present a detailed study of the emission from a z = 2.35 galaxy that causes damped Lyman α absorption in the spectrum of the background quasar (QSO), SDSS J2222−0946. We present the results of ...extensive analyses of the stellar continuum covering the rest frame optical-UV regime based on broad-band Hubble Space Telescope (HST) imaging, and of spectroscopy from VLT/X-Shooter of the strong emission lines: Lyα, O ii, O iii, N ii, Hα and Hβ. We compare the metallicity from the absorption lines in the QSO spectrum with the oxygen abundance inferred from the strong-line methods (R
23 and N2). The two emission-line methods yield consistent results: O/H = −0.30 ± 0.13. Based on the absorption lines in the QSO spectrum a metallicity of −0.49 ± 0.05 is inferred at an impact parameter of 6.3 kpc from the centre of the galaxy with a column density of hydrogen of log (N
HI
cm−2 = 20.65 ± 0.05. The star formation rates (SFRs) of the galaxy from the UV continuum and Hα line can be reconciled assuming an amount of reddening of E(B − V) = 0.06 ± 0.01, giving an inferred SFR of 13 ± 1 M yr−1 (Chabrier initial mass function). From the HST imaging, the galaxy associated with the absorption is found to be a compact (r
e
= 1.12 kpc) object with a disc-like, elongated (axis ratio 0.17) structure indicating that the galaxy is seen close to edge-on. Moreover, the absorbing gas is located almost perpendicularly above the disc of the galaxy suggesting that the gas causing the absorption is not corotating with the disc. We investigate the stellar and dynamical masses from spectral energy distribution-fitting and emission-line widths, respectively, and find consistent results of 2 × 109 M. We suggest that the galaxy is a young proto-disc with evidence for a galactic outflow of enriched gas. This galaxy hints at how star-forming galaxies may be linked to the elusive population of damped Lyα absorbers.
Abstract
We study the mean absorption spectrum of the Damped Ly
α
(DLA) population at
z
∼ 2.6 by stacking normalized, rest-frame-shifted spectra of ∼27,000 DLA systems from the DR12 of the Baryon ...Oscillation Spectroscopic Survey (BOSS)/SDSS-III. We measure the equivalent widths of 50 individual metal absorption lines in five intervals of DLA hydrogen column density, five intervals of DLA redshift, and overall mean equivalent widths for an additional 13 absorption features from groups of strongly blended lines. The mean equivalent width of low-ionization lines increases with
N
H
i
, whereas for high-ionization lines the increase is much weaker. The mean metal line equivalent widths decrease by a factor ∼1.1–1.5 from
z
∼ 2.1 to
z
∼ 3.5, with small or no differences between low- and high-ionization species. We develop a theoretical model, inspired by the presence of multiple absorption components observed in high-resolution spectra, to infer mean metal column densities from the equivalent widths of partially saturated metal lines. We apply this model to 14 low-ionization species and to Al
iii
, S
iii
, Si
iii
, C
iv
, Si
iv
, N
v,
and O
vi
. We use an approximate derivation for separating the equivalent width contributions of several lines to blended absorption features, and infer mean equivalent widths and column densities from lines of the additional species N
i
, Zn
ii
, C
ii
*, Fe
iii
, and S
iv
. Several of these mean column densities of metal lines in DLAs are obtained for the first time; their values generally agree with measurements of individual DLAs from high-resolution, high signal-to-noise ratio spectra when they are available.
Abstract
We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a
z
= 0.89 galaxy using 580–1670 MHz observations from the MeerKAT Absorption Line ...Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (
z
= 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144
α
(and H163
α
) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21
σ
(14
σ
) significance. The RRL emission contains two main velocity components and is coincident in velocity with H
i
21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (
n
e
) and the volume-averaged path length (
ℓ
) of the ionized gas. We determine
log
(
n
e
)
=
2.0
−
0.7
+
1.0
cm
−3
and
log
(
ℓ
)
=
−
0.7
−
1.1
+
1.1
pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine
log
(
n
e
)
=
3.2
−
1.0
+
0.4
cm
−3
and
log
(
ℓ
)
=
−
2.7
−
0.2
+
1.8
pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of Σ
SFR
∼ 0.6
M
⊙
yr
−1
kpc
−2
or SFR ∼ 50
M
⊙
yr
−1
, consistent with a star-forming main-sequence galaxy of
M
⋆
∼ 10
11
M
⊙
. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities.
We report a synchronized kinematic shift of C iv and Si iv broad absorption lines (BAL) in a high-ionization, radio-loud, and X-ray bright quasar SDSS-J092345+512710 (at ∼ 2.1627). This quasar shows ...two broad absorption components (blue component at v ∼ 14,000 km s−1, and red component at v ∼ 4000 km s−1 with respect to the quasars systemic redshift). The absorption profiles of C iv and Si iv BAL of the blue component show a decrease in outflow velocity with an average deceleration rate of cm s−2 and cm s−2 over a rest-frame time span of 4.15 yr. We do not see any acceleration-like signature in the red component. This is consistent with dramatic variabilities usually seen at high velocities. During our monitoring period the quasar has shown no strong continuum variability. We suggest the observed variability could be related to the time dependent changes in disk wind parameters like launching radius, initial flow velocity, or mass outflow rate.
We present the detection of the average H_2 absorption signal in the overall population of neutral gas absorption systems at z∼ 3 using composite absorption spectra built from the Sloan Digital Sky ...Survey-III damped Lyman α catalogue. We present a new technique to directly measure the H_2 column density distribution function $$f_{\rm H_2}(N)$$ from the average H_2 absorption signal. Assuming a power-law column density distribution, we obtain a slope $$\beta = -1.29 \pm 0.06(\rm stat) \pm 0.10 (\rm sys)$$ and an incidence rate of strong H_2 absorptions with N(H_2) ≳ 10^18 cm^−2 to be $$4.0 \pm 0.5(\rm stat) \pm 1.0 (\rm sys)\, \hbox{ per cent}$$ in H i absorption systems with N(H i) ≥10^20 cm^−2. Assuming the same inflexion point where $$f_{\rm H_2}(N)$$ steepens as at z = 0, we estimate that the cosmological density of H_2 in the column density range $$\log N(\rm H_2) ({\rm cm}^{-2})= 18{\text{--}}22$$ is $${\sim } 15\hbox{ per cent}$$ of the total. We find one order of magnitude higher H_2 incident rate in a sub-sample of extremely strong damped Lyman α absorption systems (DLAs) $$\log N(\rm{H\,\small {I}}) ({\rm cm}^{-2}) \ge 21.7$$, which, together with the derived shape of $$f_{\rm H_2}(N)$$, suggests that the typical H i–H_2 transition column density in DLAs is log N(H)(cm^−2) ≳ 22.3 in agreement with theoretical expectations for the average (low) metallicity of DLAs at high-z.
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