Strong Lyα Emission Research Articles

The Hubble Space Telescope colours of high-redshift Population III galaxies with strong Lyα emission

ABSTRACT Population III (pop III) galaxies, made partly or exclusively of metal-free stars, are predicted to exist at high redshifts and may produce very strong Lyα emission. A substantial fraction of these Lyα photons are likely absorbed in the intergalactic medium at z > 6, but recent simulations suggest that significant Lyα emission may be detectable up to z≈ 8.5, i.e. well into the reionization epoch. Here, we argue that high-redshift pop III galaxies with strong Lyα emission can be identified in Hubble Space Telescope imaging data because of their unusual colours. We quantify this effect in some of the filters used in Y-band dropout searches for galaxies at z≈ 8 and find that pop III galaxies with high Lyα fluxes may exhibit much bluer J−H colours at z≈ 8–10 than any normal type of galaxy at these redshifts. This colour signature can arise even if pop III stars account for as little as ∼10−3 to 10−2 of the stellar mass in these galaxies. Some of the anomalously blue objects reported in current Y-band dropout samples do in fact meet the colour criteria for Lyα-emitting pop III galaxies.

THE REST-FRAME ULTRAVIOLET SPECTRA OF UV-SELECTED ACTIVE GALACTIC NUCLEI ATz∼ 2-3

We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ∼ 2–3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as interstellar absorption features detected in star-forming Lyman break galaxies (LBGs). We report a detection of N iv] λ1486, which has been observed in high-redshift radio galaxies, as well as in rare optically selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star-forming galaxies. Blueshifted Si iv absorption provides evidence for outflowing highly ionized gas in these objects at speeds of ∼103 km s−1, quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as the Lyα equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Lyα emission is coupled with weaker low-ionization absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool interstellar gas plays in the escape of Lyα photons. However, the AGN composite does not show the same trends between Lyα strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high redshift between star-forming galaxies and similar galaxies that host AGN activity.

The detectability of Lyα emission from galaxies during the epoch of reionization

We study the visibility of the Lyman Alpha (Lya) emission line during the Epoch of Reionization (EoR). Combining galactic outflow models with large-scale semi-numeric simulations of reionization, we quantify the probability distribution function (PDF) of the fraction of Lya photons transmitted through the intergalactic medium (IGM), T_IGM. Our study focusses on galaxies populating dark matter halos with masses of M_halo=1e10 M_sun at z=8.6, which is inspired by the recent reported discovery of a galaxy at z=8.6 with strong Lya line emission. For reasonable model assumptions, we find that winds cause T_IGM>10% [50%], for the majority of galaxies, even when the Universe is ~80% [60%] neutral by volume. Thus, the observed strong Lya emission from the reported z=8.6 galaxy is consistent with a highly neutral IGM. We also investigate the implications of the recent tentative evidence for a observed decrease in the `LAE fraction' among drop-out galaxies between z=6 and z=7. If confirmed, we show that a rapid evolution in x_HI will be required to explain this observation via the effects of reionization.

Keck spectroscopy of faint 3 < z < 7 Lyman break galaxies - I. New constraints on cosmic reionization from the luminosity and redshift-dependent fraction of Lyman α emission

We present results from a new Keck spectroscopic survey of UV-faint LBGs in the redshift range 3<z<7. Combined with earlier Keck and published ESO VLT data, our sample contains more than 600 dropouts, offering new insight into the nature of sub-L* sources typical of those likely to dominate the cosmic reionisation process. Here we use this sample to characterise the fraction of strong Lya emitters within the continuum-selected dropouts. By quantifying how the "Lya fraction" varies with redshift, we seek to constrain changes in Lya transmission associated with reionisation. In order to distinguish the effects of reionisation from other factors which affect the Lya fraction (e.g. dust, ISM kinematics), we study the luminosity and redshift-dependence of the Lya fraction over 3<z<6, when the IGM is known to be ionised. These results reveal that low luminosity galaxies show strong Lya emission much more frequently than luminous systems, and that at fixed luminosity, the prevalence of strong Lya emission increases moderately with redshift over 3 < z < 6. Based on the correlation between blue UV slopes and strong Lya emitting galaxies in our dataset, we argue that the Lya fraction trends are governed by redshift and luminosity-dependent variations in the dust obscuration, with likely additional contributions from trends in the kinematics and covering fraction of neutral hydrogen. We find a tentative decrease in the Lya fraction at z~7 based on the limited IR spectra for candidate z~7 lensed LBGs, a result which, if confirmed with future surveys, would suggest an increase in the neutral fraction by this epoch. Given the supply of z and Y-drops now available from Hubble WFC3/IR surveys, we show it will soon be possible to significantly improve estimates of the Lya fraction using optical and near-IR spectrographs, thereby extending the study conducted in this paper to 7<z<8.

THE RELATIONSHIP BETWEEN STELLAR POPULATIONS AND Lyα EMISSION IN LYMAN BREAK GALAXIES

We present the results of a photometric and spectroscopic survey of 321 Lyman break galaxies (LBGs) at z ~ 3 to investigate systematically the relationship between Lya emission and stellar populations. Lya equivalent widths (EW) were calculated from rest-frame UV spectroscopy and optical/near-infrared/Spitzer photometry was used in population synthesis modeling to derive the key properties of age, dust extinction, star formation rate (SFR), and stellar mass. We directly compare the stellar populations of LBGs with and without strong Lya emission, where we designate the former group (EW > 20 AA) as Lya emitters (LAEs) and the latter group (EW < 20 AA) as non-LAEs. This controlled method of comparing objects from the same UV luminosity distribution represents an improvement over previous studies in which the stellar populations of LBGs and narrowband-selected LAEs were contrasted, where the latter were often intrinsically fainter in broadband filters by an order of magnitude simply due to different selection criteria. Using a variety of statistical tests, we find that Lya equivalent width and age, SFR, and dust extinction, respectively, are significantly correlated in the sense that objects with strong Lya emission also tend to be older, lower in star formation rate, and less dusty than objects with weak Lya emission, or the line in absorption. We accordingly conclude that, within the LBG sample, objects with strong Lya emission represent a later stage of galaxy evolution in which supernovae-induced outflows have reduced the dust covering fraction. We also examined the hypothesis that the attenuation of Lya photons is lower than that of the continuum, as proposed by some, but found no evidence to support this picture.

HUBBLE SPACE TELESCOPE DISCOVERY OF A z = 3.9 MULTIPLY IMAGED GALAXY BEHIND THE COMPLEX CLUSTER LENS WARPS J1415.1+36 AT z = 1.026

We report the discovery of a multiply lensed Ly Alpha (Lya) emitter at z = 3.90 behind the massive galaxy cluster WARPS J1415.1+3612 at z = 1.026. Images taken by the Hubble Space Telescope(HST) using ACS reveal a complex lensing system that produces a prominent, highly magnified arc and a triplet of smaller arcs grouped tightly around a spectroscopically confirmed cluster member. Spectroscopic observations using FOCAS on Subaru confirm strong Lya emission in the source galaxy and provide redshifts for more than 21 cluster members, from which we obtain a velocity dispersion of 807+/-185 km/s. Assuming a singular isothermal sphere profile, the mass within the Einstein ring (7.13+/-0.38") corresponds to a central velocity dispersion of 686+15-19 km/s for the cluster, consistent with the value estimated from cluster member redshifts. Our mass profile estimate from combining strong lensing and dynamical analyses is in good agreement with both X-ray and weak lensing results.

Crashα: coupling continuum and line radiative transfer

The detection of lya lines from local and distant objects has always been of great importance in astrophysics. It has been extensively used as indicator of redshift, as a measurement of the star formation activity of galaxies and as a probe of their internal structure. In the last few years an increasing interest has been devoted to the search of lya emitters (LAEs) at high redshift, which are expected to be characterized by a strong lya emission, but significantly attenuated by dust absorption. Emission of lya photons from high redshift sources has also an impact on the detectability of 21~cm line from neutral hydrogen in the Intergalactic Medium (IGM). This work is focused on the study, analysis and implementation of a new radiative transfer scheme (CRLya) which, for the first time in the literature, follows simultaneously the propagation of lya and ionizing radiation self-consistently. This allows to investigate the effects of evolving ionization configurations on the propagation of lya radiation and on the shaping of the line emerging from single objects. The implementation introduces the time evolution for lya photons (a feature commonly neglected in line radiative transfer codes) and, to reduce the computational time needed to follow each scattering, adopts a statistical approach to the lya treatment by making extensive use of pre-compiled tables. I find that the emerging spectra keep memory of the ionization history which generates a given ionization configuration of the gas and, to properly account for this effect, a self-consistent joint evolution of line and ionizing continuum radiation as implemented in CRLya is necessary. As next step, I implemented new features in CRLya: a new emission system, diffuse lya photons from recombination and treatment of dust. With a new test performed on a simulated galaxy at redshift z~10, I show the ability of the code to determine the variations of the lya radiation field while the gas in which it propagates is affected by the ionizing radiation emitted by the stars within the galaxy. In this test, the lya radiation is generated by both stars and recombining ionized gas. Finally I tackle the impact of lya photon scattering on the IGM temperature. This is an important issue since lya photons could be able to heat the IGM temperature above the CMB temperature and render the 21 cm line visible in emission. In the last Chapter, I discuss the implementation of the lya heating in \CRLya and I analyze how the temperature is modified by changing the most relevant physical parameters in the simulation.

Lyα emission in high-redshift galaxies

Context. A significant fraction of the high-redshift galaxies show st rong Lyα emission lines. For redshifts z> 5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Aims. Our aim is to analyse the Lyα emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyα profile and the line strength. Methods. VLT/FORS spectra with a resolution of R≈ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyα profiles are compared with theoretical models. Results. The Lyα lines range from pure absorption (EW = -17 A) to strong emission (EW = 153 A). Most Lyα emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform mo del consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation r ates of these galaxies ranging from S FRUV = 1.2 to 63.2 M⊙yr −1 uncorrected for dust absorption. Conclusions. The Lyα emission strength of our target galaxies is found to be deter mined by the amount of dust and the kinematics of the outflowing material.

Lyα excess in high-redshift radio galaxies: a signature of star formation★

About 54 per cent of radio galaxies at z≥ 3 and 8 per cent of radio galaxies at 2 ≲z < 3 show unusually strong Lyα emission, compared with the general population of high-redshift (z≳ 2) radio galaxies. These Lyα-excess objects (LAEs) show Lyα/He ii values consistent with or above standard photoionization model predictions. We reject with confidence several scenarios to explain the unusual strength of Lyα in these objects: shocks, low nebular metallicities, high gas densities and absorption/scattering effects. We show that the most successful explanation is the presence of a young stellar population which provides the extra supply of ionizing photons required to explain the Lyα excess in at least the most extreme LAEs (probably in all of them). This interpretation is strongly supported by the tentative trend found by other authors for z≥ 3 radio galaxies to show lower ultraviolet rest-frame polarization levels, or the dramatic increase in the detection rate at submm wavelengths of z > 2.5 radio galaxies. The enhanced star formation activity in LAEs could be a consequence of a recent merger which has triggered both the star formation and the active galactic nucleus/radio activities. The measurement of unusually high Lyα ratios in the extended gas of some high-redshift radio galaxies suggests that star formation activity occurs in spatial scales of tens of kpc. We argue that, although the fraction of LAEs may be incompletely determined, both at 2 ≲z 3 than at z < 3.

Deficiency of Large Equivalent Width Lyα Emission in Luminous Lyman Break Galaxies at z ~ 5-6?

We report a deficiency of luminous Lyman break galaxies (LBGs) with a large rest-frame equivalent width (EWrest) of Lyα emission at z ~ 5-6. Combining our spectroscopic sample of LBGs at z ~ 5 and those from the literature, we found that luminous LBGs at z ~ 5-6 generally show weak Lyα emissions, while faint LBGs show a wide range of Lyα EWrest and tend to have strong (EWrest 20 A) Lyα emissions; i.e., there is a deficiency of strong Lyα emission in luminous LBGs. There seems to be a threshold UV luminosity for the deficiency; it is M1400 = -21.5 to -21.0 mag, which is close to or somewhat brighter than the M* of the UV luminosity function at z ~ 5 and 6. Since the large EWrest of Lyα emission can be seen among the faint LBGs, the ratio of Lyα emitters to LBGs may change rather abruptly with the UV luminosity. If the weakness of Lyα emission is due to dust absorption, the deficiency suggests that luminous LBGs at z = 5-6 tend to be in dusty and more chemically evolved environments and that they begin star formation earlier than faint LBGs, although other causes cannot be ruled out.

Spectroscopy of \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 $i^{\prime }$ \end{document} ‐Dropout Galaxies with an NB921‐Band Depression in the Subaru Deep Field

We report new spectroscopy of two star-forming galaxies with strong Lyα emission at z = 6.03 and 6.04 in the Subaru Deep Field. These two objects are originally selected as i'-dropouts (i' - z' > 1.5) showing an interesting photometric property, the "NB921 depression." The NB921-band (centered at 9196 Å) magnitude is significantly depressed with respect to the z'-band magnitude. The optical spectra of these two objects exhibit asymmetric emission lines at λobs ~ 8540 and ~8560 Å, suggesting that these objects are Lyα emitters at z ~ 6. The rest-frame equivalent widths of the Lyα emission of the two objects are 94 and 236 Å; the latter is the Lyα emitter with the largest Lyα equivalent width at z ≳ 6 ever spectroscopically confirmed. The spectroscopically measured Lyα fluxes of these two objects are consistent with the interpretation that the NB921 depression is caused by the contribution of the strong Lyα emission to the z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be strong Lyα emitters at 6.0 ≲ z ≲ 6.5; Galactic L and T dwarfs and NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed i'-dropout sample. Thus, the NB921-depression method is very useful for finding high-z Lyα emitters with a large Lyα equivalent width over a large redshift range, 6.0 ≲ z ≲ 6.5. Although the broadband-selected sample at z ~ 3 contains only a small fraction of objects with a Lyα equivalent width larger than 100 Å, the i'-dropout sample of the Subaru Deep Field contains a much larger fraction of such strong Lyα emitters. This may imply a strong evolution of the Lyα equivalent width from z ≳ 6 to z ~ 3.

Escape of Lyα Emission in the Starburst Galaxy Markarian 357: a Wind's Far Side

Hubble Space Telescope imaging and slitless spectroscopy are used to examine where the strong Lyα emission escapes from the interstellar medium in the starburst galaxy Mrk 357. An Hα image shows that the ionized gas is mostly in a global wind, rather than associated with the individual star-forming regions seen in the optical and UV continuum. The Lyα emission comes predominantly from the northwest side of the wind structure spatially, and shows a significant redshift relative to the optical lines. Both of these properties are signatures of seeing the line photons backscattered from the far side of a prolate or bipolar starburst wind, fitting both with escape calculations and evidence for winds in high-redshift galaxies with net Lyα emission. Scattering is most important within this wind itself, rather than involving a surrounding neutral medium, as shown by the decreasing relative redshift of the line peak from 250 to ≈30 km s-1 between the center and edge of the detected emission. The Lyα emission exhibits strong asymmetry in comparison with both the starlight and Hα structures. These results add to the evidence that kinematics, rather than gas metallicity or dust content, are the dominant effect in determining which galaxies have strong Lyα emission, and that powerful (and perhaps episodic) starbursts are common among Lyman break galaxies as well as those discovered from Lyα line emission.

The nature of the Ly$\mathsf{\alpha}$-emission region of FDF-4691

In order to study the origin of the strong Lya emission of high-redshift starburst galaxies we observed and modeled the rest-frame UV spectrum and the Lya emission of the z = 3.304 galaxy FDF-4691 (rest-frame EW Lyα = 103 A). The observations show that FDF-4691 is a young starburst galaxy with a (for this redshift) typical metallicity. The broad, double-peaked profile of the Lya emission line can be explained assuming a highly turbulent emission region in the inner part of the starburst galaxy, and a surrounding extended shell of low-density neutral gas with a normal dust/gas ratio and with Galactic dust properties. The detection of the Lya emission line is explained by the intrinsic broad Lya emission and a low HI column density of the neutral shell. A low dust/gas ratio in the neutral shell is not needed to explain the strong Lya line.

The Search for Galaxy Clustering around a Quasar Pair at z =4.25 Found in the Sloan Digital Sky Survey

We present an investigation of the environment (≈600 kpc radius) of a pair of luminous z = 4.25 quasars, SDSS J1439-0034A and B, separated by 33''. An analysis of high-quality Subaru spectra of the quasars suggests that this configuration is indeed a physical pair and not a gravitational lens; the redshifts are slightly different (although marginally consistent with being the same), and the two spectra have strikingly different features. We search for bright galaxies (L 0.4L*) having similar redshifts using the V dropout technique and semi-narrowband imaging looking for strong Lyα emission. We find no enhancement in the galaxy density around the quasar pair; its environment differs very little from a general field, with the upper limit of the density enhancement being about 3.5 at a 90% confidence. We infer that bright quasars happened to appear in two normal galaxies in a general field.

GRB 021004: A Possible Shell Nebula around a Wolf‐Rayet Star Gamma‐Ray Burst Progenitor

The rapid localization of GRB 021004 by the HETE-2 satellite allowed nearly continuous monitoring of its early optical afterglow decay, as well as high-quality optical spectra that determined a redshift of z3 = 2.328 for its host galaxy, an active starburst galaxy with strong Lyα emission and several absorption lines. Spectral observations show multiple absorbers at z3A = 2.323, z3B = 2.317, and z3C = 2.293 blueshifted by ~450, ~990, and ~3155 km s-1, respectively, relative to the host galaxy Lyα emission. We argue that these correspond to a fragmented shell nebula that has been radiatively accelerated by the gamma-ray burst (GRB) afterglow at a distance ≳0.3 pc from a Wolf-Rayet star GRB progenitor. The chemical abundance ratios indicate that the nebula is overabundant in carbon and silicon. The high level of carbon and silicon is consistent with a swept-up shell nebula gradually enriched by a carbon-rich late-type Wolf-Rayet progenitor wind over the lifetime of the nebula prior to the GRB onset. The detection of statistically significant fluctuations and color changes about the jetlike optical decay further supports this interpretation, since fluctuations must be present at some level as a result of irregularities in a clumpy stellar wind medium or if the progenitor has undergone massive ejection prior to the GRB onset. This evidence suggests that the mass-loss process in a Wolf-Rayet star might lead naturally to an iron core collapse with sufficient angular momentum that could serve as a suitable GRB progenitor. Even though we cannot rule out definitely the alternatives of a dormant QSO, large-scale superwinds, or a several hundred year old supernova remnant responsible for the blueshifted absorbers, these findings point to the likelihood of a signature for a massive-star GRB progenitor.

The Effects of UV Continuum and Ly Radiation on the Chemical Equilibrium of T Tauri Disks

We show in this Letter that the spectral details of the far-ultraviolet (FUV) radiation fields have a large impact on the chemistry of protoplanetary disks surrounding T Tauri stars. We show that the strength of a realistic stellar FUV field is significantly lower than typically assumed in chemical calculations and that the radiation field is dominated by strong line emission, most notably Lyα radiation. The effects of the strong Lyα emission on the chemical equilibrium in protoplanetary disks have previously been unrecognized. We discuss the impact of this radiation on molecular observations in the context of a radiative transfer model that includes both direct attenuation and scattering. In particular, Lyα radiation will directly dissociate water vapor and may contribute to the observed enhancements of CN/HCN in disks.

Constraints to the evolution of Ly-αbright galaxies betweenz= 3 andz= 6

Galaxies at high redshift with a strong Ly-α emission line trace massive star formation in the absence of dust, and can therefore be regarded as a prime signature of the first major starburst in galaxies. We report results of the Ly-α search within the Calar Alto Deep Imaging Survey (CADIS). With the imaging Fabry-Perot interferometer, CADIS can detect emission lines in three waveband windows free of night-sky emission lines at 700 nm, 820 nm, and 920 nm. The typical flux detection limit for Ly-α emission redshifted into these windows, Flim > 3 × 10 −20 Wm −2 , corresponds to (unobscured) star formation rates of >10 M� /yr at z = 6. Candidate Ly-α-emitting galaxies are selected from the total emission line sample, which contains more than 97% of objects at z 5 than the assumption of a non-evolving population would predict. Therefore we conclude that the Ly-α bright phase of primeval star formation episodes reached its peak at redshifts 3 < z < 6.

Active Nuclei and Star-forming Objects at [ITAL][CLC]z[/CLC][/ITAL] ] 2: Metallicities, Winds, and Formation Histories

We present near-infrared observations of the active galactic nuclei (AGNs) and star-forming objects in the field of the radio galaxy 53W002 at z = 2.39. The star-forming objects are of special interest as candidate protogalactic objects. The 1.1–2.2 μm passbands sample the emitted-optical range at this redshift, providing new diagnostics of the structure, metal abundance, and age of the members of this grouping originally selected through Lyα emission. The star-forming objects are uniformly very blue in continuum slope, which fits with the strong Lyα emission in indicating metal abundances that are less than half solar; some are as blue as the most metal-poor local objects. They fall in a range of luminosity and metallicity that is not populated by local objects, indicating a shorter star-forming history at this early epoch. The best local analogs, such as Mrk 66 and 357, either have several times lower luminosity at comparable [O/H] or significantly higher [O/H] for comparable luminosity. Spectroscopy from the Near-Infrared Camera and Multi-Object Spectrometer yields detections of [O III] emission for two objects and interesting [O III] and Hβ limits for the rest, augmented by Hα limits from Infrared Telescope Facility imaging. These data are satisfied by model stellar populations that have been forming stars for the last 2–5 × 106 yr before z = 2.39. We do not see evidence for older preexisting stellar populations, either in the broadband colors or as redder halos in which the star-forming regions are imbedded. These results suggest that the compact star-forming objects we see at z = 2.0–2.5 are indeed early stages in the building of galaxies rather than transient star-forming events in larger pre-existing dynamical systems. The results also allow an alternative scheme, in which these are low-mass systems that are blowing winds rather than self-enriching, in which case they should fade rapidly with cosmic epoch. For the three prominent AGNs at z = 2.39, Hα and [O III] emission were measured. Unlike the fainter star-forming objects, their line ratios (specifically Lyα/Hα) show metallicities just as high as in nearby systems. If the AGNs occur in those systems that started with the highest density and began active star formation before the less massive surrounding objects, they will have higher metallicity (as we see in their emitted-ultraviolet line ratios). The "ionization cones" seen prominently in Lyα also appear in [O III] and Hα, with a role for continuum reflection in some cases as well. The contrast between the AGNs and fainter star-forming objects can be broadly accommodated in a hierarchical formation picture, although there are still important unknowns as to the fate of the star-forming objects.

The Dust Temperature of the “Dusty” Radio Galaxy MG 1019+0535: Evidence for an Outflow

Radio galaxies characteristically have strong Lya emission lines. However, a few have Lya equivalent widths that are substantially weaker in relation to other emission lines. One in particular was studied by Dey etal (1995), MG 1019+0535 (z=2.765). We report on our reduction of Infrared Space Observatory (ISO}) data in the 160 micron-band for this galaxy. We also compile information on two other high redshift active galaxies with weak Lya lines, the radio galaxy TXS 0211-122, and the AGN-starburst galaxy F 10214+4724, to provide a small weak-Lya line sample. IRAS plus ISO data show that F 10214+4724 has a temperature 89 +/- 12 K. TXS 0211-122 was not detected in either the submillimeter or microwave. Submillimeter measurements of MG 1019+0535 (Cimatti etal 1998) were suggestive of a dust temperature in the range 35 K ~ 300 kpc.

The Earliest Luminous Sources and the Damping Wing of the Gunn-Peterson Trough

Recent observations of high-redshift galaxies and quasars indicate that the hydrogen component of the intergalactic medium (IGM) must have been reionized at some redshift z 6. Prior to complete reionization, sources of ultraviolet radiation will be seen behind intervening gas that is still neutral, and their spectra should show the red damping wing of the Gunn-Peterson trough. While this characteristic feature may, in principle, totally suppress the Lyα emission line in the spectra of the first generation of objects in the universe, we show here that the IGM in the vicinity of luminous quasars will be highly photoionized on several megaparsec scales as a result of the source emission of Lyman continuum photons. If the quasar lifetime is shorter than the expansion and gas recombination timescales, the volume ionized will be proportional to the total number of photons produced above 13.6 eV; the effect of this local photoionization is to greatly reduce the scattering opacity between the redshift of the quasar and the boundary of its H II region. We find that the transmission on the red side of the Lyα resonance is always greater than 50% for sources radiating a total of 1069.5 ionizing photons into the IGM. The detection of a strong Lyα emission line in the spectra of bright quasi-stellar objects shining for 107 yr cannot then be used, by itself, as a constraint on the reionization epoch. The first signs of an object radiating prior to the transition from a neutral to an ionized universe may be best searched for in the spectra of luminous sources with a small escape fraction of Lyman continuum photons into the IGM or sources with a short duty cycle.