Equivalent Widths Of Mg Research Articles

The Lockman–SpReSO project

Context. The Lockman–SpReSO project is an optical spectroscopic survey of 956 far-infrared (FIR) objects within the Lockman Hole field limited by magnitude RC(AB) < 24.5. Fe II and Mg II absorption lines have been detected in 21 out of 456 objects with a determined spectroscopic redshift in the catalogue. The redshifts of these objects are in the range 0.5 ≲ z ≲ 1.44. Aims. The aim of this study is to investigate material ejection from star-forming regions and material infall into galaxies by analysing the Fe II and Mg II absorption lines. Additionally, we explore whether the correlations found in previous studies between these galactic wind velocities, line equivalent widths (EWs), and galaxy properties such as stellar mass (M*), star formation rate (SFR), and specific star formation rate (sSFR) are valid for a sample with FIR-selected objects. The objects analysed span an M* range of 9.89 < log(M*/M⊙) < 11.50 and an SFR range of 1.01 < log(SFR) < 2.70. Methods. We performed measurements of the Mg IIλλ2796, 2803, Mg Iλ2852, Fe IIλλ2374, 82, Fe IIλλ2586, 2600, and Fe IIλ2344 spectral lines present in the spectra of the selected sample to determine the EW and velocity of the flows observed in the star-forming galaxies. Subsequently, we conducted 107 bootstrap simulations using the Spearman’s rank correlation coefficient (ρs) to explore correlations with galaxy properties. Furthermore, we calculated the covering factor, gas density, and optical depth for the measured Fe II doublets. Results. Our analysis reveals strong correlations between the EW of Mg II lines and both M* (ρs = 0.43, 4.5σ) and SFR (ρs = 0.42, 4.4σ). For the Fe II lines, we observed strong correlations between the EW and SFR (ρs ∼ 0.65, > 3.9σ), with a weaker correlation for M* (ρs ∼ 0.35, > 1.9σ). No notable correlations were found between velocity measurements of the Mg II line and M*, SFR, or sSFR of the objects (ρs ∼ 0.1). However, a strong negative correlation was found between the velocity of the Fe II lines and the SFR of the galaxies (ρs ∼ −0.45, ∼3σ). Our results align with those of previous studies, although only FIR-selected objects are investigated here. Finally, we detect a candidate ‘loitering outflow’, a recently discovered subtype of the iron low-ionisation broad absorption line (FeLoBAL) quasars, at a redshift of z = 1.4399, exhibiting emission in C III] and low line velocities (|v|≲200 km s−1).

The Low-redshift Lyman Continuum Survey: Optically Thin and Thick Mg ii Lines as Probes of Lyman Continuum Escape

The Mg ii λλ2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Lyα and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg ii or strong LyC emission. Here, we present the first study of Mg ii to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg ii, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg ii profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of ∼2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg ii emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg ii. We then find that Mg ii strongly correlates with Lyα in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg ii profiles. Furthermore, we show that, for galaxies that are categorized as Mg ii emitters, one can use the information of Mg ii, metallicity, and dust to estimate the escape fraction of LyC within a factor of ∼3. These findings confirm that Mg ii lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Lyα and LyC.

Host galaxies of ultrastrong Mg ii absorbers at z ∼ 0.5

ABSTRACT From a sample of 109 candidate ultrastrong Mg ii (USMg ii; having rest equivalent width of Mg ii, W2796 > 3.0 Å) systems at z = 0.4–0.6, we confirm 27 and identify host galaxies of 20 systems based on associated nebular line emission from our SALT observations or from Sloan Digital Sky Survey (SDSS) fiber spectra. The measured impact parameter, [O ii] luminosity, star formation rate, B-band luminosity, and stellar mass are in the ranges 7.3 ≤ D[kpc] ≤ 79, $0.2\le L_{[\mathrm{ O}\,~\small {\rm II}]}[ 10^{41}~\mathrm{ erg} \mathrm{ s}^{-1}]\le 4.5$, 2.59 ≤ SFR[M⊙yr−1] ≤ 33.51, $0.15L_B^{*}\le L_B\le 1.63L_B^{*}$, and 10.21 ≤ log[M*/ M ⊙] ≤ 11.62, respectively. The impact parameters found are larger than that predicted by the W2796 versus D relationship of the general population of Mg ii absorbers. At a given D, USMg ii host galaxies are more luminous and massive compared to typical Mg ii absorbers. However, the measured SFRs are slightly lower than that of main-sequence galaxies with same M⋆ at z ∼ 0.5. We report a correlation between $L_{[\mathrm{ O}\,\small {\rm II}]}$ and W2796 for the full population of Mg ii absorbers, driven mainly by the host galaxies of weak Mg ii absorbers that tend to have low $L_{[\mathrm{ O}\,\small {\rm II}]}$ and large impact parameters. We find at least ∼33 per cent of the USMg ii host galaxies (with a limiting magnitude of mr < 23.6) are isolated and the large W2796 in these cases may originate from gas flows (infall/outflow) in single haloes of massive but not starburst galaxies. We also find galaxy interactions could be responsible for large velocity widths in at least ∼17 per cent cases.

A complete census of circumgalactic Mg ii at redshift z ≲ 0.5

ABSTRACT This paper presents a survey of Mg ii absorbing gas in the vicinity of 380 random galaxies, using 156 background quasi-stellar objects (QSOs) as absorption-line probes. The sample comprises 211 isolated (73 quiescent and 138 star-forming galaxies) and 43 non-isolated galaxies with sensitive constraints for both Mg ii absorption and H α emission. The projected distances span a range from d = 9 to 497 kpc, redshifts of the galaxies range from z = 0.10 to 0.48, and rest-frame absolute B-band magnitudes range from MB = −16.7 to −22.8. Our analysis shows that the rest-frame equivalent width of Mg ii, Wr(2796), depends on halo radius (Rh), B-band luminosity(LB), and stellar mass (Mstar) of the host galaxies, and declines steeply with increasing d for isolated, star-forming galaxies. At the same time, Wr(2796) exhibits no clear trend for either isolated, quiescent galaxies or non-isolated galaxies. In addition, the covering fraction of Mg ii absorbing gas 〈κ〉 is high with 〈κ〉 ≳ 60 per cent at <40 kpc for isolated galaxies and declines rapidly to 〈κ〉 ≈ 0 at d ≳ 100 kpc. Within the gaseous radius, the incidence of Mg ii gas depends sensitively on both Mstar and the specific star formation rate inferred from H α. Different from what is known for massive quiescent haloes, the observed velocity dispersion of Mg ii absorbing gas around star-forming galaxies is consistent with expectations from virial motion, which constrains individual clump mass to $m_{\rm cl} \gtrsim 10^5 \, \rm M_\odot$ and cool gas accretion rate of $\sim 0.7\!-\!2 \, \mathrm{ M}_\odot \, \rm yr^{-1}$. Finally, we find no strong azimuthal dependence of Mg ii absorption for either star-forming or quiescent galaxies. Our results demonstrate that multiple parameters affect the properties of gaseous haloes around galaxies and highlight the need of a homogeneous, absorption-blind sample for establishing a holistic description of chemically enriched gas in the circumgalactic space.

MAGiiCAT IV. KINEMATICS OF THE CIRCUMGALACTIC MEDIUM AND EVIDENCE FOR QUIESCENT EVOLUTION AROUND RED GALAXIES

ABSTRACT The equivalent widths of Mg II ?> absorption in the circumgalactic medium (CGM) trace the global star formation rate up to z < 6, are larger for star-forming galaxies than passively evolving galaxies, and decrease with increasing distance from the galaxy. We delve further into the physics involved by investigating gas kinematics and cloud column density distributions as a function of galaxy color, redshift, and projected distance from the galaxy (normalized by galaxy virial radius, D/R vir). For 39 isolated galaxies at 0.3 < z gal < 1.0, we have detected Mg II ?> absorption in high-resolution (Δv ≃ 6.6 km s−1) spectra of background quasars within a projected distance of 7 < D < 190 kpc. We characterize the absorption velocity spread using pixel-velocity two-point correlation functions. Velocity dispersions and cloud column densities for blue galaxies do not differ with redshift nor with D/R vir. This suggests that outflows continually replenish the CGM of blue galaxies with high velocity dispersion, large column density gas out to large distances. Conversely, absorption hosted by red galaxies evolves with redshift where the velocity dispersions (column densities) are smaller (larger) at z gal < 0.656. After taking into account larger possible velocities in more massive galaxies, we find that there is no difference in the velocity dispersions or column densities for absorption hosted by red galaxies with D/R vir. Thus, a lack of outflows in red galaxies causes the CGM to become more quiescent over time, with lower velocity dispersions and larger column densities toward lower z gal. The quenching of star formation appears to affect the CGM out to D/R vir = 0.75.

THE K GIANT STARS FROM THE LAMOST SURVEY DATA. I. IDENTIFICATION, METALLICITY, AND DISTANCE

We present a support vector machine classifier to identify the K giant stars from the LAMOST survey directly using their spectral line features. The completeness of the identification is about 75% for tests based on LAMOST stellar parameters. The contamination in the identified K giant sample is lower than 2.5%. Applying the classification method to about 2 million LAMOST spectra observed during the pilot survey and the first year survey, we select 298,036 K giant candidates. The metallicities of the sample are also estimated with uncertainty of $0.13\sim0.29$\,dex based on the equivalent widths of Mg$_{\rm b}$ and iron lines. A Bayesian method is then developed to estimate the posterior probability of the distance for the K giant stars, based on the estimated metallicity and 2MASS photometry. The synthetic isochrone-based distance estimates have been calibrated using 7 globular clusters with a wide range of metallicities. The uncertainty of the estimated distance modulus at $K=11$\,mag, which is the median brightness of the K giant sample, is about 0.6\,mag, corresponding to $\sim30$% in distance. As a scientific verification case, the trailing arm of the Sagittarius stream is clearly identified with the selected K giant sample. Moreover, at about 80\,kpc from the Sun, we use our K giant stars to confirm a detection of stream members near the apo-center of the trailing tail. These rediscoveries of the features of the Sagittarius stream illustrate the potential of the LAMOST survey for detecting substructures in the halo of the Milky Way.

ON THE LACK OF CORRELATION BETWEEN Mg II 2796, 2803 Å AND Lyα EMISSION IN LENSED STAR-FORMING GALAXIES

We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line emission in five bright star-forming galaxies at 1.66<z<1.91 that have been gravitationally lensed by foreground galaxy clusters. All five galaxies show prominent Mg II emission and absorption in a P Cygni profile. We find no correlation between the equivalent widths of Mg II and Lyman alpha emission. The Mg II emission has a broader range of velocities than do the nebular emission line profiles; the Mg II emission is redshifted with respect to systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted. The reddest components of Mg II and Lyman alpha emission have tails to 500-600 km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman alpha equivalent widths, the differing velocity profiles, and the high ratios of Mg II to nebular line fluxes together suggest that the bulk of Mg II emission does not ultimately arise as nebular line emission, but may instead be reprocessed stellar continuum emission.

Do damped and sub-damped Lyman-alpha absorbers arise in galaxies of different masses?

We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra differ intrinsically in metallicity, and whether they could arise in galaxies of different masses. Using the recent measurements of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm that sub-DLAs have higher mean metallicities than DLAs, especially at z ≲ 2. We find that the intercept of the metallicity-redshift relation derived from Zn and S is higher than that derived from Fe by 0.5–0.6 dex. We also show that, while there is a correlation between the metallicity and the rest equivalent width of Mg II λ2796 or Fe II λ2599 for DLAs, no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II selection criteria employed in the discovery of both types of systems at lower redshifts, the difference between metallicities of DLAs and sub-DLAs appears to be real and not an artefact of selection. This conclusion is supported by our simulations of Mg II λ2796 and Fe II λ2599 lines for a wide range of physical conditions. On examining the velocity spreads of the absorbers, we find that sub-DLAs show somewhat higher mean and median velocity spreads (Δ v), and an excess of systems with Δ v > 150 km s −1, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and thick disk stars, possibly suggesting different stellar populations. The absorber data appear to be consistent with galaxy down-sizing. The data are also consistent with the relative number densities of low-mass and high-mass galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on average than DLAs.

EDDINGTON RATIO GOVERNS THE EQUIVALENT WIDTH OF Mg II EMISSION LINE IN ACTIVE GALACTIC NUCLEI

We have investigated the ensemble regularities of the equivalent widths (EWs) of Mg II lambda 2800 emission line of active galactic nuclei (AGNs), using a uniformly selected sample of 2092 Seyfert 1 galaxies and quasars at 0.45 <= z <= 0.8 in the spectroscopic data set of the Sloan Digital Sky Survey Fourth Data Release. We find a strong correlation between the EW of Mg II and the AGN Eddington ratio (L/L(Edd)): EW(Mg II) proportional to (L/L(Edd))(-0.4). Furthermore, for AGNs with the same L/L(Edd), their EWs of Mg II show no correlation with luminosity, black hole mass, or line width, and the Mg II line luminosity is proportional to continuum luminosity, as expected by photoionization theory. Our result shows that Mg II EW is not dependent on luminosity, but is solely governed by L/L(Edd).

The kinematic signature of damped Lyman alpha systems: using theD-index to screen for high column density H i absorbers★

Using a sample of 21 damped Lyman alpha systems (DLAs) and 35 sub-DLAs, we evaluate the D-index from high-resolution spectra of the Mg iiλ 2796 profile. This sample represents an increase in the sub-DLA statistics by a factor of 4 over the original D-index sample. We investigate various techniques to define the velocity spread (Δv) of the Mg ii line to determine an optimal D-index for the identification of DLAs. The success rate of DLA identification is 50–55 per cent, depending on the velocity limits used, improving by a few per cent when the column density of Fe ii is included in the D-index calculation. We recommend the set of parameters that are judged to be most robust, have a combination of high DLA identification rate (57 per cent) and low DLA miss rate (6 per cent) and most cleanly separate the DLAs and sub-DLAs (Kolmogorov–Smirnov probability 0.5 per cent). These statistics demonstrate that the D-index is the most efficient technique for selecting low-redshift DLA candidates: 65 per cent more efficient than selecting DLAs based on the equivalent widths of Mg ii and Fe ii alone. We also investigate the effect of resolution on determining the N(H i) of sub-DLAs. We convolve echelle spectra of sub-DLA Lyα profiles with Gaussians typical of the spectral resolution of instruments on the Hubble Space Telescope and compare the best-fitting N(H i) values at both the resolutions. We find that the fitted H i column density is systematically overestimated by ∼0.1 dex in the moderate-resolution spectra compared to the best fits to the original echelle spectra. This offset is due to blending of nearby Lyα clouds that are included in the damping wing fit at low resolution.

Origin and Properties of Strong Mg II Quasar Absorption Line Systems

Strong Mg II quasar absorption line systems provide us with a useful tool to understand the gas that plays an important role in galaxy formation. In this paper, placing the theories of galaxy formation in a cosmological context, we present semi-analytic models and Monte-Carlo simulations for strong Mg II absorbers produced in gaseous galactic haloes and/or galaxy discs. We investigate the redshift path density for the Mg II absorption lines and the properties of galaxy/absorber pairs, in particular the anti-correlation between the equivalent width of Mg II absorption line and the projected galaxy-to-sightline distance. The simulated result of the mean redshift path density of strong Mg II systems is consistent with the observational result. The fraction of strong Mg II systems arising from galaxy disks is predicted to be ∼10% of the total. There exists an anti-correlation between the absorption line equivalent and the projected distance of sightline to galaxy center and galaxy luminosity. We determined that the mean absorbing radius Rabs ≈ 29 h−1 kpc (LB/LB*)0.35. After taking selection effects into consideration, this becomes Rabs ≈ 38 h−1 kpc (LB/LB*)0.18, which is in good agreement with the observational result. This shows the importance of considering selection effects when comparing models with observations.

Lack of Iron Abundance Evolution in High‐Redshift QSOs

We analyze the spectra of 12 high-redshift QSOs in the region of Mg II λ2798. Two six-spectrum composites, with z=4.47 and 3.35, are compared with the Francis et al. Large Bright Quasar Survey (LBQS) composite (z~0.8) and show remarkable similarity. The equivalent width of Mg II is somewhat larger in the LBQS composite than in the high-redshift composites; this may be identified as a weak Baldwin effect. The equivalent width of the Fe II blends to either side is the same in the z=3.35 composite as in the LBQS composite and marginally larger in the z=4.47 composite. We derive strong confidence limits on the absence of a significant increase in either the Fe II equivalent width or the Fe II/Mg II line ratio from the earliest epoch to the present. Hamann & Ferland predicted that the Fe II/Mg II ratio at high redshift should be a factor of ~3 lower than for low-redshift QSOs if the age of the universe at the earlier epoch is much less than 1 Gyr. This is due to the delayed contribution of supernovae type Ia to the iron abundance. A 1 Gyr minimum age of the universe at z=4.47 gives interesting upper limits to q0 for a given H0 (e.g., q0<0.20 for H0=75 km s-1 Mpc-1). The lack of change in Fe II/Mg II between the two high-redshift epochs indicates that 1 Gyr may be an underestimate of the universe age at z=4.47. We also discuss alternate explanations. The abundance evolution in the central regions of galaxies that host QSOs may follow a significantly different path to that in the solar neighborhood, perhaps from the dominance of short-lived type Ia supernovae progenitors or through the lack of any significant type Ia contribution, in which case we are yet underestimating the efficiency of Fe+ ions in QSO broad-line clouds for production of the observed Fe II. Cosmologies with terms beyond zero-pressure matter are also briefly discussed. These considerations notwithstanding, the lack of observed Fe II evolution at high redshifts puts unique constraints on luminous QSO broad-line physics, nucleosynthesis in the QSO host galaxies, and/or cosmological parameters.

Space Telescope Imaging Spectrograph Near-Ultraviolet Time-tagged Spectra of the Crab Pulsar

We present the spectrum and the pulse profile of the Crab Pulsar in the near-ultraviolet (1600-3200 A) observed with the Space Telescope Imaging Spectrograph (STIS) during the Hubble Space Telescope (HST) second Servicing Mission Orbital Verification (SMOV) period. The two-dimensional near-ultraviolet Multianode Microchannel Array (NUV MAMA) was used in time-tag mode with a 2''×2'' aperture and the low-dispersion grating, G230L, to obtain a cube with axes of slit position, wavelength, and time. The observation-derived pulse period is consistent with radio measurements, and the pulse profile agrees well with previous NUV broadband measurements by the High Speed Photometer. The pulsar spectrum includes the 2200 A dust absorption feature, plus several interstellar absorption lines. Dereddening the spectrum using the Savage-Mathis model with E(B-V)=0.55±0.05 leads to a good fit to a power law with slope αν = -0.3±0.2. The spectra of the main pulse, the interpulse, and the individual rising and falling edges are similar to the total spectrum within the limits of photon statistics. The four pulse profiles produced by breaking the spectrum into 400 A bins show the pulse profile to be stable across the NUV spectral range. Histogram analysis reveals no evidence for the superpulses seen at radio wavelengths. The interstellar absorption-line equivalent widths of Mg I, Mg II, and Fe II are lower than expected based on the implied H I column density from E(B-V)=0.5. While several explanations are possible, additional studies will be necessary to narrow the options.

Investigations of Redshifted Clouds with the 21 cm Line

21 cm studies, with the 305 m telescope at Arecibo, of QSO absorption-line clouds are described. A search for 21 cm absorption in 16 redshift systems exhibiting Mg II and Fe II absorption yield a single detection; at za = 0.394 985 in PKS 1229-02. The null observations are interpreted in terms of turbulent gas that is optically thick in the resonance transitions, but thin to 21 cm radiation. Occasionally a very opaque cloud with low velocity dispersion is present which gives rise to 21 cm absorption. The latter has little effect on saturated equivalent widths. Hence one cannot predict 21 cm absorption from properties of Mg II and Fe II absorption.Lα absorption, however, is sensitive to the presence of very opaque clouds, and a 21 cm absorption line was discovered at zA = 1.776 42 on the basis of strong Lα absorption in MC3 1331 + 170. Comparison between the Lα and 21 cm absorption spectra restricts the hydrogen spin temperature to Ts < 103 K. When combined with optical limits on fine-structure excitation this restricts the distance separating the absorber from the QSO to d > 1 kpc. However, Lα photons produced by the QSO can control Ts in the absorber, in which case d is not so restricted. Calculations of Lα transport through the absorber predict a characteristic emission feature that is observable if d ∼ 1 kpc. Sensitive observations do indicate a feature, but one which is easier to interpret in terms of an intervening galaxy at zA.A search for 21 cm emission from extended H I envelopes in a complete sample of 28 spiral galaxies is described. So far, 21 cm emission is found in only 9% of the sample galaxies, and of these in only 1 isolated galaxy, NGC 628. The upper limits restrict the equivalent width of Mg II absorption to be smaller than that normally detected in QSOs. Thus Mg II absorption lines cannot arise in galaxies like those in our sample unless Mg+/H I ≳ 0.3X(Mg).. The gas detected in NGC 628 is 100 kpc from the nucleus, and might be an intergalactic cloud.The coincidence of 21 cm and optical absorption redshifts imply space-time invariance of certain physical constants throughout most of the observable universe. Because one of these depends on all the details of strong interaction physics, it is suggested that all physical laws are globally invariant.