Observations of the radio galaxy MRC 0316–257 at $z = 3.13$ and the surrounding field are presented. Using narrow- and broad-band imaging obtained with the VLT, 77 candidate Lyα emitters with a ...rest-frame equivalent width of >15 Å were selected in a ∼7´$\,\times\,7$´ field around the radio galaxy. Spectroscopy of 40 candidate emitters resulted in the discovery of 33 emission line galaxies of which 31 are Lyα emitters with redshifts similar to that of the radio galaxy, while the remaining two galaxies turned out to be $\ion{O}{ii}$ emitters. The Lyα profiles have widths (FWHM) in the range of 120–800 km s-1, with a median of 260 km s-1. Where the signal-to-noise was large enough, the Lyα profiles were found to be asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an $\ion{H}{i}$ mass of at least $2 \times 10^2 {-} 5 \times 10^4$ M$_{\odot}$. Besides that of the radio galaxy and one of the emitters that is a QSO, the continuum of the emitters is faint, with luminosities ranging from 1.3 L* to <0.03 L*. The colors of the confirmed emitters are, on average, very blue. The median UV continuum slope is $\beta = -1.76$, bluer than the average slope of LBGs with Lyα emission ($\beta \sim -1.09$). A large fraction of the confirmed emitters (∼2/3) have colors consistent with that of dust-free starburst galaxies. Observations with the Advanced Camera for Surveys on the Hubble Space Telescope show that the emitters that were detected in the ACS image have a range of different morphologies. Four Lyα emitters (∼25%) were unresolved with upper limits on their half light radii of $r_{\rm h} < 0.6-1.3$ kpc, three objects (∼19%) show multiple clumps of emission, as does the radio galaxy, and the rest (∼56%) are single, resolved objects with $r_{\rm h} < 1.5$ kpc. A comparison with the sizes of Lyman break galaxies at $z \sim 3$ suggests that the Lyα emitters are on average smaller than LBGs. The average star formation rate of the Lyα emitters is 2.6 M$_{\odot}\;{\rm yr}^{-1}$ as measured by the Lyα emission line or <3.9 M$_{\odot}\;{\rm yr}^{-1}$ as measured by the UV continuum. The properties of the Lyα galaxies (faint, blue and small) are consistent with young star forming galaxies which are still nearly dust free. The volume density of Lyα emitting galaxies in the field around MRC 0316–257 is a factor of $3.3^{+0.5}_{-0.4}$ larger compared with the density of field Lyα emitters at that redshift. The velocity distribution of the spectroscopically confirmed emitters has a dispersion of 640 km s-1, corresponding to a FWHM of 1510 km s-1, which is substantially smaller than the width of the narrow-band filter (${\it FWHM} \sim 3500$ km s-1). The peak of the velocity distribution is located within 200 km s-1 of the redshift of the radio galaxy. We conclude that the confirmed Lyα emitters are members of a protocluster of galaxies at $z \sim 3.13$. The size of the protocluster is unconstrained and is larger than $3.3 \times 3.3$ Mpc2. The mass of this structure is estimated to be >$3{-}6 \times 10^{14}$ M$_{\odot}$ and could be the progenitor of a cluster of galaxies similar to e.g. the Virgo cluster.
ABSTRACT
The Southern Photometric Local Universe Survey (S-PLUS) is an ongoing survey of ∼9300 deg2 in the southern sky in a 12-band photometric system. This paper presents the second data release ...(DR2) of S-PLUS, consisting of 514 tiles covering an area of 950 deg2. The data has been fully calibrated using a new photometric calibration technique suitable for the new generation of wide-field multifilter surveys. This technique consists of a χ2 minimization to fit synthetic stellar templates to already calibrated data from other surveys, eliminating the need for standard stars and reducing the survey duration by ∼15 per cent. We compare the template-predicted and S-PLUS instrumental magnitudes to derive the photometric zero-points (ZPs). We show that these ZPs can be further refined by fitting the stellar templates to the 12 S-PLUS magnitudes, which better constrain the models by adding the narrow-band information. We use the STRIPE82 region to estimate ZP errors, which are ≲ 10 mmags for filters J0410, J0430, g, J0515, r, J0660, i, J0861 and z; ≲ 15 mmags for filter J0378; and ≲ 25 mmags for filters u and J0395. We describe the complete data flow of the S-PLUS/DR2 from observations to the final catalogues and present a brief characterization of the data. We show that, for a minimum signal-to-noise threshold of 5, the photometric depths of the DR2 range from 19.1 to 20.5 mag (measured in Petrosian apertures), depending on the filter. The S-PLUS DR2 can be accessed from the website: https://splus.cloud.
We present deep HST ACS observations in unk toward the z = 4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Ly alpha emitters (LAEs). We select 66 g sub(475) band ...dropouts to unk = 27, 6 of which are also LAEs. Although our color-color selection results in a relatively broad redshift range centered on z - 4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma ) in the projected pair counts at separations of theta < 10" is interpreted as being due to physical pairs. The LAEs are young (a few times 10 super(7) yr), small ((r sub(bl)) unk 0.13") galaxies, and we derive a mean stellar mass of similar to 10 super(8)-10 super(9) M unk based on a stacked K sub(s) band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g sub(475) -dropouts and find no evidence for a difference between galaxies near TN J1338-1942 and in the field. We conclude that environmental trends as observed in clusters at much lower redshift are either not yet present or washed out by the relatively broad selection in redshift. The large galaxy overdensity, its corresponding mass overdensity, and the subclustering at the approximate redshift of TN J1338-1942 suggest the assemblage of a >10 super(14) M unk structure, confirming that it is possible to find and study cluster progenitors in the linear regime at z unk 4.
We study the stellar mass assembly of the Spiderweb galaxy (MRC 1138−262), a massive z= 2.2 radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby ...protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by z= 0, increasing its stellar mass by up to a factor of ≃2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores.
We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Here we compare GALEX UV and visible-NIR images of 189 nearby (D < 40 Mpc) S0-Sm galaxies Included ...in the GALEX Atlas of Nearby Galaxies and present the first catalog of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type 1 objects ( unk 20% incidence) have structured, UV-bright/optically faint emission features in the outer disk, beyond the traditional star formation threshold. Type 2 XUV-disk galaxies ( similar to 10% incidence) exhibit an exceptionally large, UV-bright/optically low surface brightness (LSB) zone having blue UV-K sub(S) outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance. If the activity occurring in XUV-disks is episodic, a higher fraction of present-day spirals could be influenced by such outer disk star formation. Type 1 disks are associated with spirals of all types, whereas Type 2 XUV-disks are predominantly found In late-type spirals. Type 2 XUV-disks are forming stars quickly enough to double their (currently low) stellar mass in the next Gyr (assuming a constant star formation rate). XUV-disk galaxies of both types are systematically more gas-rich than the general galaxy population. Minor external perturbation may stimulate XUV-disk incidence, at least for Type 1 objects. XUV-disks are the most actively evolving galaxies growing via inside-out disk formation in the current epoch, and may constitute a segment of the galaxy population experiencing significant, continued gas accretion from the intergalactic medium or neighboring objects.
We study the environments of six radio galaxies at 2.2 < z < 2.6 using wide-field near-infrared images. We use colour cuts to identify galaxies in this redshift range, and find that three of the ...radio galaxies are surrounded by significant surface overdensities of such galaxies. The excess galaxies that comprise these overdensities are strongly clustered, suggesting they are physically associated. The colour distribution of the galaxies responsible for the overdensity is consistent with those of galaxies that lie within a narrow redshift range at z∼ 2.4. Thus the excess galaxies are consistent with being companions of the radio galaxies. The overdensities have estimated masses in excess of 1014 M⊙, and are dense enough to collapse into virialized structures by the present day; these structures may evolve into groups or clusters of galaxies.
A flux-limited sample of protocluster galaxies with K < 20.6 mag is derived by statistically subtracting the foreground and background galaxies. The colour distribution of the protocluster galaxies is bimodal, consisting of a dominant blue sequence, comprising 77 ± 10 per cent of the galaxies and a poorly populated red sequence. The blue protocluster galaxies have similar colours to local star-forming irregular galaxies (U−V
AB∼ 0.6), suggesting that most protocluster galaxies are still forming stars at the observed epoch. The blue colours and lack of a dominant protocluster red sequence imply that these cluster galaxies form the bulk of their stars at z≲ 3.
Radio galaxy PKS 1138-262 is a massive galaxy at z = 2.16, located in a dense environment. We have found an overdensity of Ly alpha emitting galaxies in this field, consistent with a proto-cluster ...structure associated with the radio galaxy. Recently, we have discovered forty candidate H alpha emitters by their excess near infrared narrow band flux. Here, we present infrared spectroscopy of nine of the brightest candidate H alpha emitters. All these candidates show an emission line at the expected wavelength. The identification of three of these lines with H alpha is confirmed by accompanying N II emission. The spectra of the other candidates are consistent with H alpha emission at z similar to 2.15, one being a QSO as indicated by the broadness of its emission line. The velocity dispersion of the emitters (360 km s super(-1)) is significantly smaller than that of the narrow band filter used for their selection (1600 km s super(-1)). We therefore conclude that the emitters are associated with the radio galaxy. The star formation rates (SFRs) deduced from the H alpha flux are in the range 6-44 M sub( )yr super(-1) and the SFR density observed is 5-10 times higher than in the HDF-N at z = 2.23. The properties of the narrow emission lines indicate that the emitters are powered by star formation and contain very young (<100 Myr) stellar populations with moderately high metallicities.
We have used the European very long baseline interferometry (VLBI) Network (EVN) to observe a sample of Lyman break analogues (LBAs), nearby (z < 0.3) galaxies with properties similar to the more ...distant Lyman break galaxies (LBGs). The study of LBGs may help define the feedback relationship between black holes (BHs) and their host galaxies. Previous Very Large Array (VLA) observations have shown that the kpc-scale radio emission from LBAs is dominated by starbursts. The main targets of this VLBI experiment were selected because they possessed emission-line properties between starbursts and Type 2 (obscured) active galactic nuclei (AGN). Eight targets (three star-forming LBAs, four composite LBAs and one Type 1 AGN) were observed at 5 GHz, four of which (one star-forming LBA and three composite LBAs) were also observed at 1.7 GHz. One star-forming LBA and one composite LBA were detected above 5σ at 1.7 GHz (only), while the AGN was detected at 5 GHz. In both LBAs, the radio luminosity (L
R) exceeds that expected from supernovae (remnants) based on a comparison with Arp 220, Arp 229A and Mrk 273, by factors of
. The composite LBA exhibits a compact core emitting around 10 per cent of the VLA flux density. The high T
b of 3.5 × 107 K and excess core L
R with respect to the L
R/L
X relation of radio-quiet AGN indicate that this LBA possesses an obscured AGN (M
BH∼ 105 − 7 M⊙). In three other composite LBAs detected previously in the X-ray, no radio sources were detected, indicating either variability or the presence of an obscured AGN below our radio sensitivity. While weak AGN may coexist with the starbursts as shown in at least one of the LBAs, their contribution to the total radio flux is fairly minimal. Our results show that the detection of such weak AGN presents a challenge at radio, X-ray and optical emission-line wavelengths at z∼ 0.2, indicating the great difficulties that need to be overcome in order to study similar processes at high redshift when these types of galaxies were common.
We present detailed images of diffuse ultraviolet (UV) intergalactic light (IGL), situated in a 60-kpc halo that surrounds the radio galaxy MRC 1138−262 at z= 2. We discuss the nature of the IGL and ...rule out faint cluster galaxies, nebular continuum emission, synchrotron, inverse Compton, synchrotron self-Compton emission and scattering of galactic stellar light as possible sources of the IGL. Dust-scattered quasar light is an unlikely possibility that cannot be ruled out entirely. We conclude that the source of the IGL is most likely to be a young stellar population distributed in a halo encompassing the radio and satellite galaxies, undergoing star formation at a rate greater than 57 ± 8 M⊙ yr−1. Within 70 kpc of the radio core, approximately 44 per cent of the star formation that is traced by UV light occurs in this diffuse mode. The average UV colour of the IGL is bluer than the average galaxy colour, and there is a trend for the IGL to become bluer with increasing radius from the radio galaxy. Both the galaxies and the IGL show a UV colour–surface brightness relation which can be obtained by variations in either stellar population age or extinction. These observations show a different, but potentially important mode of star formation, which is diffuse in nature. Star formation, as traced by UV light, occurs in two modes in the high-redshift universe: one in the usual Lyman-break galaxy clump-like mode on kpc scales, and the other in a diffuse mode over a large region surrounding massive growing galaxies. Such a mode of star formation can easily be missed by high angular resolution observations that are well suited for detecting high surface brightness compact galaxies. Extrapolating from these results, it is possible that a significant amount of star formation occurs in large extended regions within the haloes of the most massive galaxies forming at high redshift.
We present the first results obtained using a tunable narrow-band filter in the search for high-z protoclusters. Using the recently commissioned red tunable filter on the Gran Telescopio Canarias, we ...have searched for Lyα emitters in a 75 arcmin2 field centred on the z= 4.413 radio galaxy 6C0140+326. With three different wavelength tunings, we find a total of 27 unique candidate Lyα emitters. The availability of three different wavelength tunings allows us to make estimates of the redshifts for each of the objects. It also allows us to separate a possible protocluster from a structure in the immediate foreground. This division shows that the foreground region contains significantly fewer Lyα emitters. Also, the spatial distribution of the objects in the protocluster field deviates from a random distribution at the 2.5σ level. The observed redshift distribution of the emitters is different from the expected distribution of a blank field at the ∼3σ level, with the Lyα emitters concentrated near the radio galaxy at z > 4.38. The 6C0140+326 field is denser by a factor of 9 ± 5 than a blank field, and the number density of Lyα emitters close to the radio galaxy is similar to that of the z∼ 4.1 protocluster around TN J1338−1942. We thus conclude that there is an overdensity of Lyα emitters around the radio galaxy 6C0140+326. This is one of few known overdensities at such a high redshift.
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