Rest-frame Optical Emission Lines Research Articles

Lyman-break galaxies: high mass or low?

We reassess the hypothesis that Lyman-break galaxies (LBGs) at redshifts z~3 mark the centres of the most massive dark matter haloes at that epoch. First we reanalyse the kinematic measurements of Pettini et al., and of Erb et al., of the rest-frame optical emission lines of LBGs. We compare the distribution of the ratio of the rotation velocity to the central line width, against the expected distribution for galaxies with random inclination angles, modelled as singular isothermal spheres. The model fits the data well. On this basis we argue that the central line width provides a predictor of the circular velocity at a radius of several kpc. Assembling a larger sample of LBGs with measured line widths, we compare these results against the theoretical Lambda-CDM rotation curves of Mo, Mao & White, under the hypothesis that LBGs mark the centres of the most massive dark matter halos. We find that the circular velocities are over-predicted by a substantial factor, which we estimate conservatively as 1.8+/-0.4. This indicates that the model is probably incorrect. The model of LBGs as relatively low-mass starburst systems, of Somerville, Primack, and Faber (2001), provides a good fit to the data.

Physical properties of two low-luminosity $\mathsf{{\vec z} \sim 1.9}$ galaxies behind the lensing cluster AC 114

We present VLT/ISAAC near-infrared spectroscopy of two gravitationally-lensed z ~ 1.9 galaxies, A2 and S2, located behind the cluster AC 114. Thanks to large magnification factors, we have been successful in detecting rest-frame optical emission lines in star-forming galaxies 1 to 2 magnitudes fainter than in previous studies of Lyman break galaxies (LBGs) at z ~ 3. From the Ha luminosity, we estimate star formation rates (SFRs) which are 7 to 15 times higher than those inferred from the UV continuum flux at 1500 ang without dust extinction correction. The behavior of S2 and A2 in terms of O/H and N/O abundance ratios are very different, and they are also different from typical LBGs at z ~ 3. S2 is a low-metallicity object (Z ~ 0.03 Zsun) with a low N/O ratio, similar to those derived in the most metal-poor nearby HII galaxies. In contrast, A2 is a high-metallicity galaxy (Z ~ 1.3 Zsun) with a high N/O abundance ratio, similar to those derived in the most metal-rich starburst nucleus galaxies. The virial masses, derived from emission-line widths, are 0.5 and 2.4 x 10^10 Msun, for S2 and A2 respectively. Thanks to the gravitational amplification, the line profiles of S2 are spatially resolved, leading to a velocity gradient of +- 240 km/s, which yields a dynamical mass of ~ 1.3 x 10^10 Msun within the inner 1 kpc radius. Combining these new data with the sample of LBGs at z ~ 3, we conclude that these three galaxies exhibit different physical properties in terms of SFRs, abundance and mass-to-light ratios, and reddening. High-redshift galaxies of different luminosities could thus have quite different star formation histories (abridged version).

Near-ir integral field spectroscopy of high-Z galaxies

Here we summarize the exciting prospect of near-infrared spatially-resolved spectroscopy of highredshift galaxies. This is now possible with the new integral field units on 8 m-class telescopes, such as the Cambridge IR Panoramic Survey Spectrograph (CIRPASS, Parry et al.: 2001, SPIE 4008, 1193). Line emission should be an instantaneous tracer of star formation activity, but measurements based on Lyman-α are unreliable because of the selective extinction of this resonant UV line. Using more robust lines such as Hα forces a move to the near-infrared at z > 1. Great sensitivity can be achieved in the J- and H-bands (1.2 & 1.6 µm) by pre-selecting galaxies with redshifts for which prominent rest-frame optical emission lines fall into these near-infrared windows, between atmospheric lines. On an 8 m-class telescope, star formation rates of < 1 M ⊙ yr−1 will be reached at z ≈ 1.4 with Hα in the H-band. Such star formation rates are well below L* for the high-z Lyman-break population, and are comparable locally to the luminous giant H II complexes in M 101. Line ratio indices will reveal the metallicity and extinction in star forming regions within the galaxy disks. The line widths and velocity offsets will provide a sensitive probe of the kinematics of the galaxies, to explore the evolution of fundamental scaling relations. Combining this spatially-resolved spectroscopy with deep, multi-colour, high-resolution imaging (e.g. from HST) will explore fundamental structural parameters (2D rotation velocity profiles, stellar masses, sizes and disk scale lengths), luminosities and star formation rates, and study their evolution with redshift. This will provide a stringent test of current models for the formation and evolution of galactic disks.

Near‐Infrared Spectroscopy of Two Galaxies atz = 2.3 andz = 2.9: New Probes of Chemical and Dynamical Evolution at High Redshift

This study presents Keck optical and infrared spectroscopy of the rest-frame ultraviolet and optical emission lines in two Lyα-emitting galaxies at z > 2. These data provide insight on the evolution of fundamental galaxy scaling relations at early epochs, especially the luminosity-velocity and luminosity-metallicity relations. Spectral diagnostics suggest that the Coup Fourre galaxy at z = 2.3 and Lynx 2-9691, a serendipitously discovered, luminous Lyman drop galaxy at z = 2.9, are star-forming galaxies without active nuclei. Lynx 2-9691 exhibits extended [O III] emission over a diameter of greater than 28 kpc, reminiscent of the Lyα nebulae discovered near Lyman drop galaxies. We estimate star formation rates of 59 and 111 M☉ yr-1, respectively, from Balmer recombination line luminosities, 2-3 times higher than inferred from the ultraviolet continuum. The ratios of strong nebular emission lines indicate subsolar oxygen abundances in the range 8.2 < 12 + log(O/H) < 8.8 (Z = 0.25-0.95 Z☉). Interestingly, Galactic metal-rich globular clusters have similar metallicities, consistent with the idea that we could be seeing the formation of galaxies like the Milky Way at z ~ 3. The measured gas-phase oxygen abundances are greater than 4-10 times higher than the Z < 0.1 Z☉ metallicities found in damped Lyα (DLA) absorbers at similar redshifts, indicating that DLA systems trace fundamentally different environments than the vigorously star-forming objects observed here. If this intense star formation activity represents the dominant formation episodes for stars in today's spiral bulges or ellipticals, then the evolved descendants in the local universe should exhibit similarly subsolar metallicities in their dominant stellar populations that formed 8-10 Gyr ago. When these new data are combined with a sample of four other high-redshift spectroscopic results from the literature, we find that star-forming galaxies at z ~ 3 are 2-4 mag more luminous than local spiral galaxies of similar metallicity and thus are offset from the local luminosity-metallicity relation. Their kinematic line widths are σv = 65-130 km s-1, making this sample 1-3 mag more luminous than local galaxies of similar line width and mass. Less luminous Lyman drop galaxies need to be studied to see if these deviations are universal or apply to only the most luminous high-redshift galaxies.

A Statistical Study of Rest‐Frame Optical Emission Properties in Luminous Quasars at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $2.0\leq z\leq 2.5$ \end{document}

We have obtained H-band spectra of 32 luminous quasars at 2.0≤z≤2.5 with the Multiple Mirror Telescope. The sample contains 15 radio-loud quasars (RLQs) and 17 radio-quiet quasars (RQQs). We have measured emission line properties from the rest-frame wavelength range of approximately λλ4500-5500 by fitting the data with composite model spectra. Our analysis includes comparison of RLQs versus RQQs, as well as comparison between the broad-absorption-line quasar (BALQSO) and non-broad-absorption-line quasar (nonBALQSO) subsets of the RQQ sample. In addition, we calculated the complete correlation matrix of the measured properties. We combined our high-redshift sample with the sample of 87 low-redshift quasars from Boroson & Green to determine the luminosity and redshift dependences of the measured emission properties. Our main results are the following: (1) The RLQ sample has significantly (at more than 97.2% confidence) stronger [O III] λ5007 emission than the RQQ sample, which favors scenarios including two populations of quasars that are intrinsically different. We are not aware of a unified model based upon orientation that can explain enhanced [O III] emission with increased radio power. (2) The RLQ sample has significantly narrower (in full width at half-maximum) Hβ broad component line profiles than the RQQ sample. (3) At the sensitivity of our observations, there are no statistically significant (>95%) differences between the rest-frame optical emission line properties of the BALQSO and nonBALQSO subsamples. This result is consistent with the view that all RQQs have broad-absorption-line clouds with a small (~10%-20%) covering factor and that differences between the two types are merely a function of viewing angle and covering factor. (4) The significant [O III]-Fe II anticorrelation found in lower redshift quasars holds at this higher redshift range; however, it is the [O III] emission in this relationship that appears to be related to the physical distinction between the RLQ and RQQ classes instead of the Fe II emission that distinguishes at low redshifts and luminosities. We also find significant relationships between (i) the [O III] emission strength and the radio power, the broad-emission-line widths, and the X-ray continuum shape; (ii) positive correlations relating the strength of optical Fe II emission to broad-emission-line widths and the shape of the ionizing continuum; and (iii) similar relations for the strength and width of the Hβ emission. Many of these correlations have been found in lower redshift and luminosity studies. (5) We report a previously unknown luminosity and/or redshift dependence of the narrow-line region velocity width over the range 0<z<2.5, such that emission line widths increase with increasing luminosity. We confirm a similar dependence for the Hβ broad-line width. These findings may be evidence for a physical connection between the continuum and line-emitting regions at similar energies. Furthermore, we find a Baldwin Effect for the [O III] λ5007 line in the RQQ-only sample over this same range in redshifts.

Infrared Observations of Nebular Emission Lines from Galaxies atz≃ 3

We present the first results from a program of near-infrared spectroscopy aimed at studying the familiar rest-frame optical emission lines from the H II regions of Lyman break galaxies at z 3. By targeting redshifts that bring the lines of interest into gaps between the strong OH sky emission, we have been successful in detecting Balmer and [O III] emission lines in all five galaxies observed so far with CGS4 on UKIRT. The typical line fluxes are a few times 10-17 ergs s-1 cm-2, approximately 1 order of magnitude lower than the limits reached with wide-field narrowband imaging surveys. For a Salpeter initial mass function and a H0 = 70 km s-1 Mpc-1, q0 = 0.1 cosmology, the Hβ luminosities uncorrected for dust extinction imply star formation rates of 20-270 M☉ yr-1; these values are greater than those that may have been deduced from the ultraviolet continuum luminosities at 1500 A by factors of between ~0.7 and ~7. Uncertainties in the shape of the reddening curve and in the intrinsic UV continuum slope do not yet allow us to assess accurately the level of dust extinction; however, on the basis of the present limited sample, it appears that an extinction of 1-2 mag at 1500 A may be typical of Lyman break galaxies. This value is consistent with recent estimates of dust obscuration in star-forming galaxies at z ≤ 1 and does not require a substantial revision of the broad picture of star formation over the Hubble time proposed by Madau and coworkers in 1996. In four out of five cases the velocity dispersion of the emission line gas is σ 70 km s-1, while in the fifth the line widths are nearly three times larger. Virial masses Mvir ≈ (1-5) × 1010 M☉ are suggested, but both velocities and masses could be higher, because our observations are only sensitive to the brightest cores of these systems where the line widths may not sample the full gravitational potential. The relative redshifts of interstellar absorption, nebular emission, and Lyα emission lines differ by several hundred km s-1 and suggest that large-scale outflows may be a common characteristic of Lyman break galaxies. The forthcoming availability of high-resolution infrared spectrographs on large telescopes will soon allow all of these questions to be addressed in much greater detail.

SEARCHES FOR DISTANT GALAXIES

ABSTRACT This thesis presents the results of an extensive search for star-forming galaxies at high redshift. By imaging through narrow-band filters (3-5000 {km s}-1) in the near-infrared K-band, this survey is sensitive to the rest-frame optical emission lines at z>2, which are indicators of star formation. Previous searches have mainly been based on Lyman-α, but are probably fundamentally flawed as this resonantly-scattered line is selectively quenched, and is known to be weak or absent in many star-forming galaxies at high redshift.

A Narrowband Imaging Survey for High Redshift Galaxies in the Near Infrared

A narrowband imaging survey of 276 square minutes of arc was carried out at near infrared wavelengths to search for emission line objects at high redshifts. Most of the fields contained a known quasar or radio galaxy at a redshift that placed one of the strong, restframe optical emission lines (H-alpha, [O III], H-beta, or [O II]) in the bandpass of the narrowband filter. The area weighted line flux limit over the entire survey was 3.4x10e-16 erg/cm2/s (3-sigma), while the most sensitive limits reached 1.4x10e-16 erg/cm2/s. Integrating the volume covered by all four optical emission lines in each image yields a total comoving volume surveyed of 1.4x10e5 cubic megaparsecs. Considering only H-alpha emission in the K band (2.05 < z < 2.65), where the survey is most sensitive, the survey covered a comoving volume of 3.0x10e4 cubic megaparsecs to a volume-weighted average star formation rate of 112 M-solar/yr (for Ho = 50 km/s/Mpc, Omega = 1). This is the most extensive near-infrared survey which is deep enough to have a reasonable chance at detecting strong line emission from an actively star-forming population of galaxies, when d against simple models of galaxy formation. One emission line candidate was identified in this survey, and subsequently confirmed spectroscopically.

Optical lines in high-redshift quasi-stellar objects - Balmer lines, forbidden O III, and Fe II

We present infrared spectroscopy of familiar rest-frame optical emission lines in the four bright z∼2.5 QSOs Q0933+733, Q1255+317, Q1246-057, and Q1413+117. The spectral regions around Hα and around Hβ, including the [O III] λλ5007, 4959 lines and optical Fe II complexes, were observed with sufficient resolution and sensitivity to allow the deblending of the different features. We discuss the emission-line properties of these QSOs in the context of their lower redshift, lower luminosity counterparts. The rest-frame optical Fe II complexes around Hβ are detected in high redshift QSOs for the first time, and are particularly strong compared to lower redshift objects