Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConstraining Dust and Molecular Gas Properties in Lyman Alpha Blobs at z~3
204
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In order to constrain the bolometric luminosities, dust properties and molecular gas content of giant Lyman alpha nebulae, the so-called Lyman alpha blobs, we have carried out a study of dust continuum and CO line emission in two well-studied representatives of this population at z ~ 3: a Lya blob discovered by its strong Spitzer MIPS 24um detection (LABd05; Dey et al. 2005) and the Steidel blob 1 (SSA22-LAB01; Steidel et al. 2000). We find that the spectral energy distribution of LABd05 is well described by an AGN-starburst composite template with L(FIR) = (4.0 +/- 0.5) x 10^12 Lsun, comparable to high-z sub-millimeter galaxies and ultraluminous infrared galaxies. New APEX/LABOCA 870um measurements rule out the reported SCUBA detection of the SSA22-LAB01 (S[850um] = 16.8 mJy) at the > 4sigma level. Consistent with this, ultra-deep Plateau de Bure Interferometer (PdBI) observations with ~2arcsec spatial resolution also fail to detect any 1.2mm continuum source down to ~0.45mJy per beam (3sigma). Combined with the existing (sub)mm observations in the literature, we conclude that the FIR luminosity of SSA22-LAB01 remains uncertain. No CO line is detected in either case down to integrated flux limits of (Snu dV) < 0.25--1.0 Jy km/s, indicating a modest molecular gas reservoir, M(H_2) < 1--3 x 10^10 Msun. The non-detections exclude, with high significance (12 sigma), the previous tentative detection of a CO(4-3) line in the SSA22-LAB01. The increased sensitivity afforded by ALMA will be critical in studying molecular gas and dust in these interesting systems.
rate research
Read More
Ly-alpha blobs (LABs) offer insight into the complex interface between galaxies and their circumgalactic medium. Whilst some LABs have been found to contain luminous star-forming galaxies and active galactic nuclei that could potentially power the Ly-alpha emission, others appear not to be associated with obvious luminous galaxy counterparts. It has been speculated that LABs may be powered by cold gas streaming on to a central galaxy, providing an opportunity to directly observe the `cold accretion mode of galaxy growth. Star-forming galaxies in LABs could be dust obscured and therefore detectable only at longer wavelengths. We stack deep SCUBA-2 observations of the SSA22 field to determine the average 850um flux density of 34 LABs. We measure S_850 = 0.6 +/- 0.2mJy for all LABs, but stacking the LABs by size indicates that only the largest third (area > 1794 kpc^2) have a mean detection, at 4.5 sigma, with S_850 = 1.4 +/- 0.3mJy. Only two LABs (1 and 18) have individual SCUBA-2 > 3.5 sigma detections at a depth of 1.1mJy/beam. We consider two possible mechanisms for powering the LABs and find that central star formation is likely to dominate the emission of Ly-alpha, with cold accretion playing a secondary role.
We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGN). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest frame far infrared) also indicates a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with sub-mm detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with the Lya luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs.
We constrain the distribution of spatially offset Lyman-alpha emission (Ly$alpha$) relative to rest-frame ultraviolet emission in $sim300$ high redshift ($3<z<5.5$) Lyman-break galaxies (LBGs) exhibiting Ly$alpha$ emission from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep Survey and Chandra Deep Field South fields (${simeq0.2}~mathrm{deg}^2$ total). Because slit spectroscopy compresses two-dimensional spatial information into one spatial dimension, we use Bayesian inference to recover the underlying Ly$alpha$ spatial offset distribution. We model the distribution using a 2D circular Gaussian, defined by a single parameter $sigma_{r,mathrm{Ly}alpha}$, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample ($3<z<5.5$), we find $sigma_{r,mathrm{Ly}alpha}=1.70^{+0.09}_{-0.08}$ kpc ($68%$ conf.), corresponding to $sim0.25$ arcsec at $langle zrangle=4.5$. We also find that $sigma_{r,mathrm{Ly}alpha}$ decreases significantly with redshift. Because Ly$alpha$ spatial offsets can cause slit-losses, the decrease in $sigma_{r,mathrm{Ly}alpha}$ with redshift can partially explain the increase in the fraction of Ly$alpha$ emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If $sigma_{r,mathrm{Ly}alpha}$ continues to decrease into the reionization epoch, then the decrease in Ly$alpha$ transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the IGM, slit losses may explain some of the drop in Ly$alpha$ transmission observed at $z>6$. Spatially resolved observations of Ly$alpha$ and UV continuum at $6<z<8$ are needed to settle the issue.
We present spectroscopic measurements of the [OIII] emission line from two subregions of strong Lyman-alpha emission in a radio-quiet Lyman-alpha blob (LAB). The blob under study is LAB1 (Steidel et al. 2000) at z ~ 3.1, and the [OIII] detections are from the two Lyman break galaxies embedded in the blob halo. The [OIII] measurements were made with LUCIFER on the 8.4m Large Binocular Telescope and NIRSPEC on 10m Keck Telescope. Comparing the redshift of the [OIII] measurements to Lyman-alpha redshifts from SAURON (Weijmans et al. 2010) allows us to take a step towards understanding the kinematics of the gas in the blob. Using both LUCIFER and NIRSPEC we find velocity offsets between the [OIII] and Lyman-alpha redshifts that are modestly negative or consistent with 0 km/s in both subregions studied (ranging from -72 +/- 42 -- +6 +/- 33 km/s). A negative offset means Lyman-alpha is blueshifted with respect to [OIII], a positive offset then implies Lyman-alpha is redshifted with respect to [OIII]. These results may imply that outflows are not primarily responsible for Lyman alpha escape in this LAB, since outflows are generally expected to produce a positive velocity offset (McLinden et al. 2011). In addition, we present an [OIII] line flux upper limit on a third region of LAB1, a region that is unassociated with any underlying galaxy. We find that the [OIII] upper limit from the galaxy-unassociated region of the blob is at least 1.4 -- 2.5 times fainter than the [OIII] flux from one of the LBG-associated regions and has an [OIII] to Lyman-alpha ratio measured at least 1.9 -- 3.4 times smaller than the same ratio measured from one of the LBGs.
We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the SSA22 protocluster and in several blank fields. The total survey area is 2.1 square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2} for the Ly-alpha images, we construct a sample of 14 LAB candidates with major-axis diameters larger than 100 kpc, including five previously known blobs and two known quasars. This survey triples the number of known LABs over 100 kpc. The giant LAB sample shows a possible morphology-density relation: filamentary LABs reside in average density environments as derived from compact Ly-alpha emitters, while circular LABs reside in both average density and overdense environments. Although it is hard to examine the formation mechanisms of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate to cold gas accretion from the surrounding inter-galactic medium (IGM) and more circular LABs may relate to large-scale gas outflows, which are driven by intense starbursts and/or by AGN activities. Our survey highlights the potential usefulness of giant LABs to investigate the interactions between galaxies and the surrounding IGM from the field to overdense environments at high-redshift.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
