PDF superior Ly alpha emission line galaxies at z=3 1 in the extended Chandra Deep Field South

Ly alpha emission line galaxies at z=3 1 in the extended Chandra Deep Field South

Ly alpha emission line galaxies at z=3 1 in the extended Chandra Deep Field South

With an integral-field spectrograph, it is also possible to in- crease the sample of high-redshift galaxies by identifying objects with equivalent widths lower than our detection threshold of 80 8 (20 8 in the LAE rest frame). However, the gain in doing so is likely to be small: according to Figure 9, Ly rest-frame equivalent widths e-fold with a scale length of 75 8 . If this law extrapolates to weaker lined systems, as suggested by the models of Le Delliou et al. ( 2006), then most LAEs are already being detected, and pushing the observations to lower equivalent widths will only increase the number counts by 20%. Further- more, as the data of Hogg et al. ( 1998) demonstrate, contami- nation by foreground [O ii ] objects increases rapidly once the equivalent width cutoff drops below 50 8 in the observers frame (or 12 8 in the rest frame of Ly). Unless one can accept a large increase in the fraction of contaminants, surveys for high-redshift galaxies need to either stay above this threshold or extend to the near-IR (to detect H and [O iii ] k5007 in the interlopers).
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13 Lee mas

The high redshift (z > 3) active galactic nucleus population in the 4 Ms Chandra Deep Field South

The high redshift (z > 3) active galactic nucleus population in the 4 Ms Chandra Deep Field South

sources with few counts can be explained considering that these two spectral parameters have a significant degree of degeneracy. The problem is further complicated by the redshifted absorption cut- off, which moves outside the Chandra bandpass at z 3 even for significant degrees of obscuration, introducing further uncertainties. To better constrain the column density, we fixed the photon index to = 1.8 and repeated the spectral analysis on all the sources. This photon index is a widely used value for sources with low counting statistics, being considered the typical slope for AGN power-law emission in X-rays (e.g. Turner et al. 1997; Tozzi et al. 2006). The best-fitting parameters, fluxes and intrinsic luminosities derived using this spectral model are reported in Table 1. Similar results are obtained fitting simultaneously the source and background spectra. All the X-ray spectra of the sources, fitted using this model, are shown in Appendix B. The effects of assuming a flatter photon index ( = 1.6) will be discussed in Sections 3.3 and 4.
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Ly alpha EMITTING GALAXIES AT z=2 1 IN ECDF S: BUILDING BLOCKS OF TYPICAL PRESENT DAY GALAXIES?

Ly alpha EMITTING GALAXIES AT z=2 1 IN ECDF S: BUILDING BLOCKS OF TYPICAL PRESENT DAY GALAXIES?

EW > 20 Å (Hogg et al. 1998) and the small volume available for z 0 objects. Local universe [O ii ] emitters would be several arcseconds across, so would stand out clearly in our catalogs. In any case, the exclusion of GALEX-detected sources should rule out this contribution. 4. Obscured AGN, which are capable of triggering a narrow- band excess through their narrow emission lines. Since we found 10 AGNs as X-ray sources in the Chandra catalog and some of those may be obscured or Compton thick, and most models predict a roughly equal number of obscured and unobscured AGN at this redshift (Treister et al. 2004), we set an upper limit on residual AGN contamination of 10 ± 10 objects. This will be probed via follow-up spectroscopy. Note that heavily obscured AGN may not show any emission lines at all and therefore would not be found in our sample; this reinforces confidence in our upper limit. We stacked 66 LAEs in our sample with coverage in the 2 Ms CDF-S image (Luo et al. 2008) and found 3σ upper limits for the soft-band (hard-band) stacked flux of 4 × 10 −18 (2 × 10 −17 ) erg s −1 cm −2 , corresponding to a luminosity of 1.3 ×10 41 (6.7×10 41 ) erg s − 1 at z = 2.1. The observed soft-band implies a 3σ upper limit on the average SFR of 30 M yr − 1 (Ranalli et al. 2003). Compared to our typical rest-UV SFR of 4 M yr −1 , this implies that the dust correction must be less than a factor of 7. Because individual X-ray detections above the 2 Ms flux limit of 2 × 10 −17 erg s −1 cm −2 were removed from our LAE sample in this region, any remaining AGN must have soft- band luminosity below 7×10 41 erg s −1 . In the extreme case,
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Revealing a population of heavily obscured active galactic nuclei at z approximate to 0 5 1 in the chandra deep field south

Revealing a population of heavily obscured active galactic nuclei at z approximate to 0 5 1 in the chandra deep field south

jects). The median simulated flux in the 10–30 keV band ( ≈ 3 × 10 −16 erg cm −2 s −1 ) is about two orders of magnitude below the sensitivity limit. This result is a natural conse- quence of the requirement that the sources are not individu- ally detected in the 2–8 keV band of the 4 Ms Chandra expo- sure; the extraordinarily high sensitivity of the 4 Ms CDF-S places a tight constraint on the intrinsic luminosities of the ISX sources and prevents them from being detected by NuS- TAR. Therefore, it is not likely that NuSTAR or ASTRO-H will detect any of the ISX sources presented here. However, they will probably detect some of the X-ray selected CT AGN can- didates (e.g., Tozzi et al. 2006; Comastri et al. 2011) in hard X-rays; such detections will be useful for a clear determina- tion of the intrinsic spectral shape and power of these sources. One other approach to identify heavily obscured or CT AGNs is via X-ray spectroscopy at relatively low energies (< 10 keV) complemented by multiwavelength data (e.g., Polletta et al. 2006; Tozzi et al. 2006; Alexander et al. 2008, 2011; Comastri et al. 2011). The X-ray emission of these objects is characterized by a flat continuum and often a strong rest-frame 6.4 keV iron Kα fluorescent line (e.g., Della Ceca et al. 2008; Murphy & Yaqoob 2009). For the ISX sources presented here, spectroscopic analyses are prob- ably not feasible due to the small number of counts expected. However, it is worth performing a further study of the X-ray selected CT AGN candidates in Tozzi et al. (2006), which were previously studied using only the 1 Ms CDF-S data. With the current 4 Ms CDF-S data and the 3 Ms XMM-Newton observations on the CDF-S, we will be able to constrain bet- ter their nature (e.g., Comastri et al. 2011). In the case of the CDF-S receiving further Chandra exposure (e.g., 10 Ms to- tal), some ( ≈ 15%) of the heavily obscured AGNs in the ISX sample could be detected in the HB, given the simulated prop- erties and expected 10 Ms sensitivity.
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The NuSTAR Extragalactic Surveys: Initial Results and Catalog from the Extended Chandra Deep Field South

The NuSTAR Extragalactic Surveys: Initial Results and Catalog from the Extended Chandra Deep Field South

Compton-thick fraction. Most prior studies have found that R ( usually probed indirectly via the strength of the iron K-line ) is inversely correlated with luminosity and generally weak ( i.e., R  1 ) for moderately luminous AGNs ( e.g., Iwasawa & Taniguchi 1993; Nandra et al. 1997; Page et al. 2005; Ricci et al. 2011 ) . Spectral analysis of a single source in our NuSTAR sample ( NuSTAR J033202-2746.8 in the ECDFS: Del Moro et al. 2014 ) found a moderate re fl ection component ( R ≈ 0.55 ) for this high luminosity ( L 10 40 keV - » 6.4 ´ 10 44 erg s − 1 ) source. However, Ballantyne ( 2014 ) found that strong re fl ec- tion ( R ≈ 1.7 ) at all luminosities is needed to reconcile different measurements of the local XLF across a wide range of X-ray energies (∼ 0.5 – 200 keV ) . Our measurements of the 10 – 40 keV XLF indicate that moderate-to-strong re fl ection ( R ∼ 1 − 2 ) is required to describe the average spectral characteristics of L 10 40 keV - ~ 10 43 46 - erg s − 1 AGNs at z ∼ 0.1 – 3. The extent, strength, and spectral characteristics of re fl ection provide insights into the physical nature of the obscuring material and the accretion disk ( e.g., García et al. 2013; Falocco et al. 2014; Brightman et al. 2015 ) . Strong re fl ection could also indicate a substantial population of rapidly spinning black holes in the detected sample; however, a relatively small intrinsic fraction of high-spin sources (∼ 7% ) can potentially dominate the observed number counts at a given fl ux limit ( Brenneman et al. 2011; Vasudevan et al. 2015 ) . Accurately measuring the distribution of re fl ection is thus an important challenge for future statistical studies of AGN populations.
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mips 24 mu m observations of the hubble deep field south: probing the ir radio correlation of galaxies at z > 1

mips 24 mu m observations of the hubble deep field south: probing the ir radio correlation of galaxies at z > 1

IFRSs are a class of radio sources recently discovered in the Australia Telescope Large Area Survey by Norris et al. (2006). These are radio sources brighter than a few hundred μJy at 1.4 GHz which have no observable infrared counterpart in the Spitzer Wide-area Infrared Extragalactic Survey (SWIRE; Lonsdale et al. 2004). Most have flux densities of a few hundred μJy at 1.4 GHz, but some are as bright as 20 mJy, resulting in extreme infrared to radio ratios. Recent very long baseline interferometry detections have constrained the radio sources sizes to less than 0.03 arcsec, suggesting IFRSs are compact AGNs (Norris et al. 2007; Middelberg et al. 2008). Deeper Spitzer legacy survey data in the extended Chandra Deep Field South yielded two IRAC detections of the four IFRSs in that field, and SED modeling of these sources with the new constraints showed that they are consistent with z > 1 radio- loud AGNs (Huynh et al. 2010).
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Evolution in the continuum morphological properties of Ly alpha emitting galaxies from z=3 1 TO z=2 1

Evolution in the continuum morphological properties of Ly alpha emitting galaxies from z=3 1 TO z=2 1

of a galaxy’s formation and their size evolution should be much less steep than that of the overall galaxy popula- tion. If, on the other hand, Lyα emission is able to escape from a large fraction of galaxies with previous genera- tions of stars already in place, they should more closely trace the Ferguson et al. (2004) law. The heterogeneity seen in the present samples suggests that the LAE pop- ulation contains both types of objects, but more work is needed to elucidate whether this division is an actual bimodality or simply a continuous range of properties. The z = 2.1 LAE sample, in particular, may contain up to ∼ 15% contamination from low-redshift galaxies (see Section 3.1) - spectroscopic follow-up is needed to ac- curately estimate the contamination fraction and isolate the types of objects that contribute to the contamina- tion. Furthermore, analysis of the deep rest-frame opti- cal (observed-NIR) imaging obtained as part of the Wide Field Camera 3 Early Release Science (Windhorst et al. 2010) and the Cosmic Assembly Near-infrared Deep Ex- tragalactic Legacy Survey would allow us to determine where most of the stellar mass in these objects lies and whether it coincides spatially with the rest-UV emission from the young stars.
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The chandra deep protocluster survey : Ly alpha blobs are powered by heating, not cooling

The chandra deep protocluster survey : Ly alpha blobs are powered by heating, not cooling

Figure 3. Composite spectral energy distribution of the X-ray detected LABs in SSA 22. Where shown, upper limits are at the 3σ level, and where relevant we have shown the range of luminosities in the sample to indicate variations from source-to-source. As a guide, we show the SED of Arp 220 (Silva et al. 1998) redshifted to z = 3.09 and normalized to our observed 4.5 μm luminosity. For comparison, we also show the radio quiet quasar (RQQ) template of Elvis et al. (1994) redshifted and scaled to our average X-ray flux. The UV luminosity predicted by the RQQ template is in good agreement with the X-ray/UV power-law extrapolation of Steffen et al. (2006) which we indicate as a dotted line and point at λ = 2500 Å. In the inset we show a fit to the optical–near-IR photometry using hyperz . The fit is a moderately reddened (A V ∼ 1.5 mag) continuous star formation history of age ∼ 100 Myr. This is to be compared with the intrinsic UV luminosity from the AGN
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Mid Infrared Properties and Color Selection for X Ray Detected Active Galactic Nuclei in the MUSYC Extended Chandra Deep Field South

Mid Infrared Properties and Color Selection for X Ray Detected Active Galactic Nuclei in the MUSYC Extended Chandra Deep Field South

properties of a large sample of AGNs at moderately high red- shifts selected through their X-ray emission. In the observed 3.6–8.0 m band, over half of these X-ray-selected AGNs show infrared colors consistent with those of galaxies. Across the nar- row wavelength range of the IRAC filters, most galaxies are also consistent with power-law spectral shapes. As a result, IRAC data alone are not sufficient for a complete or reliable selection of (moderate-luminosity) AGNs. At 24 m, dust from both star- forming galaxies and AGNs is detected. Unfortunately, observed IRAC to 24 m colors do not effectively separate galaxies pow- ered by AGNs from those experiencing star formation. Previous studies with IRAS have shown the far-infrared to be valuable for discriminating active from inactive galaxies (Sanders & Mirabel 1996); to apply similar techniques to present deep surveys re- quires longer wavelength data, not just at 24 m but at 70 m and, if possible, 160 m as well.
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IDENTIFICATIONS AND PHOTOMETRIC REDSHIFTS OF THE 2 Ms CHANDRA DEEP FIELD SOUTH SOURCES

IDENTIFICATIONS AND PHOTOMETRIC REDSHIFTS OF THE 2 Ms CHANDRA DEEP FIELD SOUTH SOURCES

We present reliable multiwavelength identifications and high-quality photometric redshifts for the 462 X-ray sources in the ≈2 Ms Chandra Deep Field-South (CDF-S) survey. Source identifications are carried out using deep optical-to-radio multiwavelength catalogs, and are then combined to create lists of primary and secondary counterparts for the X-ray sources. We identified reliable counterparts for 442 (95.7%) of the X-ray sources, with an expected false-match probability of ≈ 6.2%; we also selected four additional likely counterparts. The majority of the other 16 X-ray sources appear to be off-nuclear sources, sources associated with galaxy groups and clusters, high-redshift active galactic nuclei (AGNs), or spurious X-ray sources. A likelihood-ratio method is used for source matching, which effectively reduces the false-match probability at faint magnitudes compared to a simple error-circle matching method. We construct a master photometric catalog for the identified X-ray sources including up to 42 bands of UV-to-infrared data, and then calculate their photometric redshifts (photo-z’s). High accuracy in the derived photo-z’s is accomplished owing to (1) the up-to-date photometric data covering the full spectral energy distributions (SEDs) of the X-ray sources, (2) more accurate photometric data as a result of source deblending for ≈10% of the sources in the infrared bands and a few percent in the optical and near-infrared bands, (3) a set of 265 galaxy, AGN, and galaxy/AGN hybrid templates carefully constructed to best represent all possible SEDs, (4) the Zurich Extragalactic Bayesian Redshift Analyzer used to derive the photo-z’s, which corrects the SED templates to best represent the SEDs of real sources at different redshifts and thus improves the photo-z quality. The reliability of the photo-z’s is evaluated using the subsample of 220 sources with secure spectroscopic redshifts. We achieve an accuracy of |Δ z | /(1 + z) ≈ 1% and an outlier [with |Δ z | /(1 + z) > 0.15] fraction of ≈ 1.4% for sources with spectroscopic redshifts. We performed blind tests to derive a more realistic estimate of the photo-z quality for sources without spectroscopic redshifts. We expect there are ≈ 9% outliers for the relatively brighter sources (R 26), and the outlier fraction will increase to ≈ 15%–25% for the fainter sources (R 26). The typical photo-z accuracy is ≈6%–7%. The outlier fraction and photo-z accuracy do not appear to have a redshift dependence (for z ≈ 0–4). These photo-z’s appear to be the best obtained so far for faint X-ray sources, and they have been significantly (50%) improved compared to previous estimates of the photo-z’s for the X-ray sources in the ≈2 Ms Chandra Deep Field-North and ≈1 Ms CDF-S. Key words: cosmology: observations – galaxies: active – galaxies: distances and redshifts – galaxies: photometry – X-rays: galaxies
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The Chandra Deep Protocluster Survey: Evidence for an Enhancement in the AGN Activity in the SSA22 Protocluster at z = 3 09

The Chandra Deep Protocluster Survey: Evidence for an Enhancement in the AGN Activity in the SSA22 Protocluster at z = 3 09

We present results from a new ultra-deep ≈ 400 ks Chandra observation of the SSA22 protocluster at z = 3.09. We have studied the X-ray properties of 234 z3 Lyman Break Galaxies (LBGs; protocluster and field) and 158 z = 3.09 Lyα Emitters (LAEs) in SSA22 to measure the influence of the high-density protocluster environment on the accretion activity of supermassive black holes (SMBHs) in these UV-selected star-forming populations. We detect individually X-ray emission from active galactic nuclei (AGNs) in six LBGs and five LAEs; due to small overlap between the LBG and LAE source population, ten of these sources are unique. At least six and potentially eight of these sources are members of the protocluster. These sources have rest-frame 8–32 keV luminosities in the range of L 8 − 32 keV = (3–50) ×10 43 ergs s −1 and an average observed-frame 2–8 keV to 0.5–2 keV band ratio (BR)
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9 Lee mas

The 4 Ms Chandra deep field south number counts apportioned by source class: pervasive active galactic nuclei and the ascent of normal galaxies

The 4 Ms Chandra deep field south number counts apportioned by source class: pervasive active galactic nuclei and the ascent of normal galaxies

We present 0.5–2 keV, 2–8 keV, 4–8 keV, and 0.5–8 keV (hereafter soft, hard, ultra-hard, and full bands, respectively) cumulative and differential number-count (log N –log S) measurements for the recently completed ≈4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of ≈1.9–4.3 times fainter than the previously deepest number-count investigations. In the soft band (SB), the most sensitive bandpass in our analysis, the ≈4 Ms CDF-S reaches a maximum source density of ≈27,800 deg −2 . By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei (AGNs), normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology) and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting SB source density of ≈14,900 deg −2 , the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits and, at the limiting SB flux, reach source densities of ≈12,700 deg −2 and make up 46% ± 5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, as well as significant normal-galaxy contributions to the overall number counts, indicates that normal galaxies will overtake AGNs just below the ≈4 Ms SB flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the ≈ 4 Ms sensitivity limit. We show that a future ≈10 Ms CDF-S would allow for a significant increase in X-ray-detected sources, with many of the new sources being cosmologically distant (z 0.6) normal galaxies.
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A public, K selected, optical to near infrared catalog of the extended chandra deep field south (ECDFS) from the multiwavelength survey by YALE Chile (MUSYC)

A public, K selected, optical to near infrared catalog of the extended chandra deep field south (ECDFS) from the multiwavelength survey by YALE Chile (MUSYC)

Figure 13. Stellar identification using Bz K colors. In each panel, we show the Bz K diagram for sources in the MUSYC ECDFS catalog (black points), and compare our Bz K star selection (dashed line) to other complimentary stellar classifications: viz., SED-classified “stars” from the COMBO-17 survey (Wolf et al. 2004, open stars), GEMS point sources (H¨aussler et al. 2007, open circles), and spectrally classified stars (open squares/red symbols). The left panel shows the agreement between Bz K selection and these other indicators; in the right panel we show where Bz K selection disagrees with other indicators. So, for example, circles in the left panel show all GEMS point sources, whereas in the right panel they show those Bz K-selected “stars” that are not GEMS point sources. In the either panel, the stellar sequence in Bz K color space can be seen to be isolated by 0.1 mag in (z − K ) from deep field galaxies. This includes QSOs, which can be seen in the left panel as GEMS point sources scattered throughout the galaxy population. Although there are a handful of spectrally classified stars lying well outside the Bz K stellar selection region (open squares in the left panel), these objects are neither COMBO-17 “stars” nor GEMS point sources (stars and circles in the right panel); i.e., the spectral classification is wrong. Of the Bz K-selected stars which are not GEMS point sources (circles in the right panel), roughly half are faint stars superposed over a diffuse background galaxy, and roughly half are faint galaxies whose photometry is significantly affected by a bright, nearby star.
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The LABOCA survey of the Extended Chandra Deep Field South: a photometric redshift survey of submillimetre galaxies

The LABOCA survey of the Extended Chandra Deep Field South: a photometric redshift survey of submillimetre galaxies

Six of the SMGs have multiple robust counterparts; of these four SMGs (LESS 2, LESS 27, LESS 49 and LESS 74) have two counterparts, which as we will show in Section 4.1, having pho- tometric redshifts consistent with them being at the same distance and thus possibly physically associated. The choice of the precise counterpart for the SMG is therefore irrelevant for these sources as their physical interpretation is not dependent upon this. However, the other two SMGs (LESS 10 and LESS 49) each has two robust counterparts with photometric redshifts and SEDs that suggest they are not physically associated. In these cases, from the information currently available, it is not possible to determine which of the two counterparts is the source of the submillimetre flux, or whether the LABOCA detection is a blend of the emission from two galaxies. To avoid bias, we have included all of the multiple counterparts in our analysis, but we note that their small number means that their inclusion does not significantly affect our results.
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Ly alpha emitting galaxies at z=3 1: L* progenitors experiencing rapid star formation

Ly alpha emitting galaxies at z=3 1: L* progenitors experiencing rapid star formation

Multi-object spectroscopy of 92 LAE candidates, along with other MUSYC targets, was performed with Magellan- Baade+IMACS on Oct. 26-27, 2003, Oct. 7-8, 2004, Feb. 4-7, 2005, Nov. 2-3, 2005, Oct. 25-27, 2006, Nov. 21-22, 2006 and Feb. 18-20, 2007. The 300 line/mm grism was used with 1.2 00 slitlets to cover 4000 − 9000Å at a resolution of R = 640 i.e., 470 km s −1 , at the wavelength of Lyα emis- sion. Mask exposure times ranged from 2 to 5 hours, with the longer exposures sufficient to detect Lyα emission lines down to our completeness limit of ∼ 1.5 × 10 −17 ergs cm −2 s −1 , as- suming clear conditions and minimal slit losses. Details of our spectroscopy will be given in P. Lira et al. (in prep). Red- shifts were confirmed to lie at 3.08 < z < 3.14 for 61 of the LAEs, with 1 interloping AGN at z = 1.60 where [C III]λ1909 falls in the narrowband filter, and the other 30 objects lacking sufficient S/N to yield redshifts. Our success rate for the slit- masks with the highest S/N was 90%, setting an upper limit of 10% on possible contamination of our LAE sample. The rate of non-detections was higher in masks with shorter exposure times resulting from weather or instrument challenges, con- sistent with the reduced S/N. Our spectroscopy shows that the sample is not contaminated by z = 0.34 [O II] emission-line galaxies, which are the typical interlopers for narrow-band- selected LAE samples. These have been eliminated by re- quiring observer’s-frame EW> 80Å which eliminates all but the rarest [O II] emitters (Terlevich et al. 1991,Hogg et al. 1998,Stern et al. 2000).
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Low ionization galaxies and evolution in a pilot survey up to z = 1

Low ionization galaxies and evolution in a pilot survey up to z = 1

In the course of an investigation of the diffuse intergalactic light in X-ray emitting clusters at in- termediate redshifts (Melnick et al. 1999), we detected a puzzling S-shaped arc-like structure in the ROSAT cluster RX J0054.0–2823 (Faure et al. 2007), which we tentatively identified as the gravi- tationally lensed image of a background galaxy at a redshift between z = 0.5 and z = 1.0. The cluster, however, is characterized by having three dominant D or cD galaxies in the center, two of which are clearly interacting. We designed an observing strategy that allowed us to simultaneously observe the arc, the diffuse Intra-Cluster Light (ICL), and a magnitude limited sample of individual galaxies in the field by taking advantage of the multi-object spectroscopic mode of the FORS2 in- strument on Paranal. By optimizing the mask design (see below), we were able to obtain: (a) very deep observations of the arc; (b) very deep long-slit observations of the ICL; and (c) redshifts and flux distributions for 654 galaxies, of which 550 are in the pencil beam and at 0.275 ≤ z ≤ 1.05 .
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Variability selected low luminosity active galactic nuclei in the 4 Ms chandra deep field south

Variability selected low luminosity active galactic nuclei in the 4 Ms chandra deep field south

An alternative possible explanation for the suppressed vari- ability at low luminosities is a change in accretion structure. Ptak et al. (1998) found a similar drop in variability strength below L 2−10 keV ≈ 2×10 41 erg s − 1 in a sample of LLAGNs and LINERs observed with ASCA on variability timescales of less than a day. The authors hypothesized that a radiatively ineffi- cient accretion flow (RIAF; e.g., Yuan & Narayan 2004) could be responsible for suppressed short-timescale variability at low luminosities due to the larger extent of the X-ray source. This scenario would not obviously explain the reduced variability on ∼month–year timescales seen here. RIAF models also predict a hard X-ray photon index due to the lack of an optically thick ac- cretion disk, which provides the soft X-ray photons. The stacked X-ray photon index for variable galaxies (Γ stack ≈ 1.93 ± 0.13;
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Radiation pressure, absorption and AGN feedback in the Chandra Deep Fields

Radiation pressure, absorption and AGN feedback in the Chandra Deep Fields

Most of our objects lie below λ ∼ 0.1 which means that the range of high Eddington ratios is not fully probed by the CDF AGN. To sample the area of λ & 0.1 requires that we look at the regions probed by investigations of the rarer luminous quasars (Fig. 7). Kollmeier et al. (2006) and Steinhardt & Elvis (2010) show that the most luminous objects in the SDSS have λ ∼ 0.2 − 0.3, but do not investigate any absorption properties. Greene et al. (2009) look at a large sample of narrow line AGN, and find that they have high Eddington ratios (∼ 0.2). Although these sources are obscured, there are no available values for their hydrogen column densities. Just et al. (2007) do study the X-ray properties of 59 of the most op- tically luminous quasars and find that each is consistent with no in- trinsic absorption and collectively are obscured by a mean column density < 2 × 10 21
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Rest frame optical emission lines in far infrared selected galaxies at z < 1 7 from the fmos cosmos survey

Rest frame optical emission lines in far infrared selected galaxies at z < 1 7 from the fmos cosmos survey

log( X ) ~ 43.3 erg s − 1 at z ~ 1.5 for the 2 – 10 keV band for the Chandra observations ) . Essentially all of X-ray detections at z > 0.5 have L X > 10 42 erg s - 1 , a luminosity level typically due to an AGN and a higher X-ray luminosity than would be expected from star formation using the relation of Mineo et al. ( 2014 ) . It should be noted that our observing program speci fi cally targeted X-ray AGNs whenever possible so the total fraction of X-ray AGNs among our ( U ) LIRGs is high. Therefore, the total AGN fractions quoted here should not be considered as absolutes, but rather the comparison between AGNs identi fi ed via the different methods is what we are interested in. For comparison, ∼ 15% – 30% of ( U ) LIRGs at this redshift in COSMOS are X-ray-detected AGNs ( Kartaltepe et al.  2010a ) . Overplotted on each panel are the lower-limit abundance sequence, the redshift-dependent AGN classi fi ca- tion line, and the starburst – AGN mixing sequence for scenarios 3 and 4 from Kewley et al. ( 2013b ) . We identify all galaxies above the AGN classi fi cation line as “ BPT-selected AGNs, ” although this new dividing line is uncertain and likely does not select all AGNs ( especially those in composite systems ) . The mixing sequences range from Scenarios 1 – 4 and span both normal and extreme ISM conditions and metal-rich and metal- poor AGN narrow-line regions ( NLRs ) at high redshift. Here, we plot scenario 3 ( extreme ISM conditions and metal-rich AGN NLRs ) and scenario 4 ( extreme ISM conditions and metal-poor AGN NLRs ) since they appear to be the best match for our high-redshift data points. The percentage of sources that fall within the bounds for scenarios 1 – 4 are 62%, 52%, 66%, and 64% at intermediate redshift and 70%, 28%, 73%, and 53% at high redshift. Scenario 2 ( normal ISM conditions and metal- poor AGN NLRs ) has the lowest fraction, while the fraction in the other three scenarios is comparable.
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The composite nature of Dust Obscured Galaxies (DOGs) at z ∼ 2–3 in the COSMOS field – I  A far infrared view

The composite nature of Dust Obscured Galaxies (DOGs) at z ∼ 2–3 in the COSMOS field – I A far infrared view

to represent an important phase in the evolution of galaxies as they are linked to the formation of massive galaxies via gas-rich star- bursting mergers followed by an AGN-driven quenching of the star formation (e.g. Sanders et al. 1988a,b). Recent studies (Dey et al. 2008; Bussmann et al. 2009, 2012) have suggested a similar evolu- tionary sequence where DOGs are an important intermediate phase between gas-rich major mergers (traced by SMGs) and quasars at z ∼ 2. These studies describe an evolutionary scenario in which the starbursting nature of SMGs evolves into the composite nature of DOGs as an underlying AGN grows; this is followed by a quasar phase that terminates star formation, leading to the formation of a passive, massive elliptical galaxy. Within this context, DOGs could provide a key insight to an extremely dusty stage in the evolution of galaxies at z ∼ 2, where both AGN and star formation activity coex- ist. Their composite nature was until relatively recently inaccessible prior to the availability of sensitive mid- to far-infrared data.
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