Top PDF The Link Between Extended Line Emission and AGN Feedback in Brightest Cluster Galaxies

The Link Between Extended Line Emission and AGN Feedback in Brightest Cluster Galaxies

The Link Between Extended Line Emission and AGN Feedback in Brightest Cluster Galaxies

In contrast, 2A 0335+096 appears to be experiencing a cooling-dominated phase of the feedback cycle. The extensive optical nebula is dominated by a clumpy bar of emission that extends to 15 − 20 kpc from the BCG. This structure resembles an approximately edge-on, disk-like formation in the gas. The line-of-sight velocity field reveals large-scale rotation of the gas in this bar about the central galaxy, with a velocity amplitude of ∼ 200 km s − 1 . We have suggested that this is a result of gas cooling and collapse throughout the inner cluster core. The inner part of the nebula is kinematically distinct from this outer rotating structure. There is a velocity shear across the nucleus and over an inner bar of bright emission that extends along a similar axis as the outer bar, but has a counter-rotational sense of motion. The nebula in this region may be associated with a nearby galaxy. Weak radio and AGN activity is present, but does not appear to have a significant effect on the surrounding gas. However, there is evidence in X-ray observations for previous episodes of AGN activity interacting with the ICM on very large scales throughout the cluster core. The X-ray cooling in this system dominates the power output of the AGN. We conclude that the BCG is undergoing a cooling and accumulation period of feedback activity.
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Constraining cold accretion on to supermassive black holes: molecular gas in the cores of eight brightest cluster galaxies revealed by joint CO and CN absorption

Constraining cold accretion on to supermassive black holes: molecular gas in the cores of eight brightest cluster galaxies revealed by joint CO and CN absorption

a function of radius significantly constrains the distance at which the gas is likely to be, as predicted by simulations such as chaotic cold accretion (Gaspari et al. 2017). These simu- lations of clumpy molecular gas condensation show that the volume filling factor and internal density of molecular clouds are both inversely proportional to radius. This means that the vast majority of dense clouds which contribute to the line of sight absorption are expected to reside in the inner region, within radii of up to ∼ 200 pc (for a broader com- parison of our results to chaotic cold accretion simulations, see § 8.3). Conversely, two properties of the absorbing clouds imply that they lie outside the approximate Bondi capture radius in each system of a few tens of parsecs. First, the fact that the clouds are detectable by CO(0-1) absorption implies that they are all relatively cool and not being sig- nificantly heated by the high radiative power of the central AGN. Given that dust grains are found with ubiquity in in- terstellar gas, the approximate level of heating a molecular gas cloud will experience can be demonstrated by providing an estimate for the equilibrium dust temperature. For a dust grain radiating with a black-body spectrum, the balance be- tween radiation and emission can be written as
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A study of high-redshift AGN feedback in SZ cluster samples

A study of high-redshift AGN feedback in SZ cluster samples

Studies of samples of systems with X-ray cavities found a strong correlation between the mechanical power injected into the hot gas by the AGN through cavities (i.e. the 4pV enthalpy of the buoyantly rising cavities) and the cooling rates of this gas (Bˆırzan et al. 2004; Dunn & Fabian 2004; Rafferty et al. 2006). From this evidence, it was postulated that the AGN are heat- ing the gas and regulating cooling through a feedback loop. This process is known as the jet-mode, maintenance-mode, or radio- mode AGN feedback and is commonly observed in the nearby universe, where no significant brightest cluster galaxy (BCG) growth typically occurs. In jet-mode AGN feedback, the accre- tion rate is thought to be well below the Eddington limit, with the bulk of the energy released in kinetic form by two-sided radio- bright jets. Galaxies with such AGN tend to be low-excitation radio galaxies (LERGs), based on the presence of weak, narrow, low-ionization emission lines (Hine & Longair 1979; Hardcastle, Evans & Croston 2006, 2007; Best & Heckman 2012). LERGs may be powered by hot-mode accretion, when the material falls directly on to the SMBH through accretion of clumps of gas (known as the cold feedback mechanism, Pizzolato & Soker 2005; Soker 2006; Pizzolato & Soker 2010; Gaspari, Ruszkowski & Sharma 2012; Gaspari, Brighenti & Temi 2015; McCourt et al. 2012; Sharma et al. 2012; Li et al. 2015; Prasad, Sharma & Babul 2015; Voit et al. 2015, 2016), with no accretion disc to ionize (see also observational support from Rafferty, McNamara & Nulsen 2008; Cavagnolo et al. 2011; Farage, McGregor & Dopita 2012; McNamara et al. 2014).
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Delayed triggering of radio active galactic nuclei in gas rich minor mergers in the local Universe

Delayed triggering of radio active galactic nuclei in gas rich minor mergers in the local Universe

Importantly, the Shabala et al. (2012) AGN classification was based on radio continuum imaging rather than optical emission-line luminosity, potentially probing a later phase in post-merger evo- lution of the host galaxy (Cowley et al. 2016). Unlike single-fibre optical spectroscopic diagnostics, radio continuum images also pro- vide spatial information about the extent of the radio jets. Extended jets are indicative of older AGN, which have potentially imparted significant feedback on SF in the host galaxy. Radio emission in galaxies can come about either due to AGN jets or supernova- driven shocks. In Shabala et al. (2012), AGN were identified as those galaxies in which the radio luminosity (drawn from the Faint Images of the Radio Sky at Twenty Centimetres, FIRST, survey; Becker, White & Helfand 1995) significantly (1.5σ ) exceeded the SDSS SFR (Brinchmann et al. 2004). While useful, this separation can suffer from misclassification due to the scatter in the SFR–radio luminosity relation. In particular, it is biased against galaxies with comparable levels of radio emission coming from SF and the AGN. Moreover, the 5.4 arcsec resolution of FIRST is comparable with the sizes of a number of galaxies in the sample, and it is therefore unclear whether the AGN has imparted any feedback on smaller scales.
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A physical model for [C II] line emission from galaxies

A physical model for [C II] line emission from galaxies

To verify that the origin of the discrepancies between the model and cloudy in the plateau region are indeed due to temperature variations within the neutral layer, we use the average temperature returned by cloudy for each metallicity when computing Λ [CII] (T) in the model. The re- sults of this test are shown in Fig. 3 (right panel). While at low metallicity (as seen also from Fig. 4) using a fixed T = 100 K provides a very good approximation, at Z > 0.1 the mean temperature is in the range T = 50 − 80 K. Once this correction is implemented in the model, its predictions almost perfectly match cloudy results over the entire range of metallicities and ionisation parameters.
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The optical/X ray connection: intra cluster medium iron content and galaxy optical luminosity in 20 galaxy clusters

The optical/X ray connection: intra cluster medium iron content and galaxy optical luminosity in 20 galaxy clusters

X-ray observations of galaxy clusters have shown that the intra-cluster gas has iron abundances of about one-third of the solar value. These observations also show that part (if not all) of the intra-cluster gas metals was produced within the member galaxies. We present a systematic analysis of 20 galaxy clusters to explore the connection between the iron mass and the total luminosity of early- and late-type galaxies, and of the brightest cluster galaxies (BCGs). From our results, the intra-cluster medium (ICM) iron mass seems to correlate better with the luminosity of the BCGs than with that of the red and blue galaxy populations. As the BCGs cannot produce alone the observed amount of iron, we suggest that ram-pressure plus tidal stripping acts together to enhance, at the same time, the BCG luminosities and the iron mass in the ICM. Through the analysis of the iron yield, we have also estimated that SN Ia are responsible for more than 50 per cent of the total iron in the ICM. This result corroborates the fact that ram-pressure contributes to the gas removal from galaxies to the ICM, being very efficient for clusters in the temperature range 2 < kT (keV) < 10.
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Abundant serendipitous emission line sources with JWST/NIRSpec

Abundant serendipitous emission line sources with JWST/NIRSpec

Our fiducial model for the evolution of the UV luminosity function is used to predict a distribution of line fluxes (H α and [O III ]) based on the method presented in Section 3. For a given exposure time, we calculate the sensitivity of NIRSpec as a function of wavelength for a spectrally unresolved point source centred in a 1 × 3 microslit. We then scale this sensitivity as a function of spatial position according to the throughput assuming a standard three-point nodding pattern (Section 4). At each spatial position we determine the fraction of the predicted line emitters that would be detectable (>5σ in [O III ] and/or H α) if the object were located at that position. Note that this ignores (1) the potential spatial extent of the objects, as they are all assumed to be intrinsically point-like and (2) the fact that extracting the flux for an off-centre and potentially newly discovered source will not necessarily result in the optimal signal-to-noise. The effects of these assumptions are discussed further in Section 6. By taking into account the total volume probed by the NIRSpec microslits, we obtain the total number of observable line emitters per MSA configuration and hence per survey.
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DDO 216 A1: a central globular cluster in a low luminosity transition type galaxy

DDO 216 A1: a central globular cluster in a low luminosity transition type galaxy

The structural parameters of the cluster resemble those of the “ faint fuzzy ” clusters found in lenticular galaxies ( Brodie & Larsen 2002 ) , but its color is much bluer and it otherwise appears typical of the globular cluster population of dwarfs. DDO 216-A1 is unusually close to the center of its host galaxy and is also unusually extended for a cluster with small projected galactocentric distance ( Sharina et al. 2005 ) . How- ever, it falls below the luminosity and surface brightness of the great majority of clusters that are most likely to be identi fi ed as galactic nuclei ( Georgiev et al. 2009a; Brodie et al. 2011 ) , although exceptions exist ( Côté et al. 2006; Georgiev & Böker 2014 ) . Sharina et al. ( 2005 ) fi nd that among dSphs with globular clusters, more than half show clusters seen in projection against the center of the galaxy. While DDO 216- A1 fi ts among these clusters in luminosity, its large radius distinguishes it from the ( usually ) compact central clusters. However, it is still quite a bit more compact than very extended clusters like Scl-dE1  GC1, with a half-light radius of 22 pc ( da Costa et al. 2009 ) .
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The Sloan Digital Sky Survey Reverberation Mapping Project : Hα and Hβ reverberation measurements from first year spectroscopy and photometry

The Sloan Digital Sky Survey Reverberation Mapping Project : Hα and Hβ reverberation measurements from first year spectroscopy and photometry

The most common methods to measure RM time lags are the interpolated cross-correlation function (ICCF; e.g., Gaskell & Peterson 1987; Peterson et al. 2004), and the discrete correlation function (DCF; Edelson & Krolik 1988) or z-transformed DCF (zDCF; Alexander 1997). The DCF has been shown to perform best when large numbers of points are present; for cases with lower sampling such as our data, it is better to use the ICCF (White & Peterson 1994). The zDCF was designed to mitigate some of the issues with the DCF; however, for this study we opted to use the ICCF, as it is more tra- ditionally used and a detailed comparison between the ICCF and zDCF is not yet available in the literature. The ICCF method works as follows: For a given time delay τ , we shift the time coordinates of the first light curve by τ and then linearly interpolate the second light curve to the new time coordinates, measuring the cross- correlation Pearson coefficient r between the two light curves using overlapping points. We next shift the second light curve by − τ and interpolate the first light curve, and average the two values of r. This process is repeated over the entire range of allowed τ , evaluating r at discrete steps in τ. This procedure allows the measurement of r as a function of τ, called the ICCF. The centroid (τ cent ) of
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Dust in high-z radio-loud AGN

Dust in high-z radio-loud AGN

Hughes, Dunlop & Rawlings 1997 for a recent review; Omont et al. 1996b; Ivison et al. 1998). At high redshift, dust is also thought to be present in damped Ly α absorption systems (Pet- tini et al. 1994; Pei, Fall & Bechtold 1991), in very red galaxies (Hu & Ridgway 1994), and in high- z radio galaxies (Cimatti 1996 and references therein). A substantial amount of dust is also expected in theoretical models of the evolution of galax- ies at high- z (Mazzei & De Zotti 1996 and references therein). Finally, it is important to recall that molecular gas has been ob- served in a few distant active galaxies, allowing a direct estimate of the dust-to-gas mass ratio at large cosmological distances for the first time (see Omont et al. 1996a; Ohta et al. 1996).
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Astronomy   Galaxies and the Expanding Universe pdf

Astronomy Galaxies and the Expanding Universe pdf

A connection between electricity and magnetism had long been suspected, and in 1820 the Danish physicist Hans Christian Orsted showed that an electric current flowing in a wire produces its own magnetic field. Andre-Marie Ampere of France immediately repeated Orsted's experiments and within weeks was able to express the magnetic forces between current-carrying conductors in a simple and elegant mathematical form. He also demonstrated that a current flowing in a loop of wire produces a magnetic dipole indistinguishable at a distance from that produced by a small permanent magnet; this led Ampere to suggest that magnetism is caused by currents circulating on a molecular scale, an idea remarkably near the modern understanding.
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An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field-South: The AGN Fraction and X-Ray Properties of Submillimeter Galaxies

An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field-South: The AGN Fraction and X-Ray Properties of Submillimeter Galaxies

10 − 15 , and >10 − 15 erg cm − 2 s − 1 , respectively. For the overlapping region of the CDF-S and E-CDF-S where each sensitivity map reports a different flux limit, the smaller one (representing the best sensitivity) was used when creating the merged sensitivity map. The large red dots mark the X-ray detected SMGs, while the blue dots are other SMGs in the ALESS main catalog. X-ray detected SMGs are labeled with their short LESS IDs (e.g., ALESS 11.1 is labeled as “11”). The same labeling convention also applies to all plots following. The small open circles are the LABOCA submm sources (Weiß et al. 2009) that were followed up by ALMA but whose fields do not contain any ALESS main- catalog source (57 such sources; see Hodge et al. 2013 for details). The inner thin solid line shows the GOODS-S region (Giavalisco et al. 2004), which is also approximately the combined coverage for Hubble WFC3 Early Release Science and CANDELS (Grogin et al. 2011) in this region. The outer thick solid line marks the region for the 4 Ms CDF-S (X11). The LABOCA region is roughly a square whose edges are ∼ 2 –3 outside the E-CDF-S boundaries. The average exposure time of the X-ray detected SMGs is 2.2 Ms, while for the X-ray undetected SMGs it is 0.8 Ms. As also discussed in Section 5, some of the non-detections are simply due to shallower X-ray coverage.
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Triggering active galactic nuclei in galaxy clusters

Triggering active galactic nuclei in galaxy clusters

AGN and star formation are triggered by processes which in- crease the supply of gas to the centres of galaxies. For example, mergers and interactions of galaxies are expected to induce AGN activity, since they provide a torque on the gas which can fun- nel it into the centre of the galaxy (Hernquist & Mihos 1995). This is supported by observations, with an observed increase in the prevalence of AGN in interacting galaxy pairs (Ellison et al. 2011; Sabater et al. 2013) and ‘lopsided’ galaxies (Reichard et al. 2009), which are indicative of galaxy interactions. Observations and sim- ulations show that mergers also trigger episodes of star formation (e.g. Doyon, Joseph & Wright 1994; Mihos & Hernquist 1996), with an AGN preceded by a starburst a common evolutionary sequence during gas-rich mergers (Hopkins et al. 2006; Melnick et al. 2015). Alongside galaxy mergers, the ram pressure that cluster galaxies experience as they move through the intracluster medium (ICM) may induce AGN and star formation. This pressure is able to strip gas from galaxies (ram pressure stripping), which may cause tails of stripped gas to form behind the galaxy as it moves in the clus- ter, as has been observed for galaxies in the Virgo cluster (e.g. Kenney, van Gorkom & Vollmer 2004; Crowl et al. 2005; Chung et al. 2007). Ram pressure stripping leads to a decreased preva- lence of radiative-mode AGN activity in the centres of clusters (Ellison et al. 2011; Ehlert et al. 2014; Khabiboulline et al. 2014), since the ram pressure has depleted the gas supply of these central galaxies. However, models and hydrodynamical simulations show that lower ram pressures can compress the gas in the galaxy, and actually induce star formation (e.g. Fujita & Nagashima 1999; Kro- nberger et al. 2008; Kapferer et al. 2009; Tonnesen & Bryan 2009; Bekki 2014), which is also supported by observations (e.g. Lee et al. 2017). These moderate ram pressures could also conceivably lead to higher black hole accretion, and hence trigger AGN activity, since ram pressure can lead to angular momentum loss in gas clouds (Tonnesen & Bryan 2009) and trigger gravitational instability in the galactic disc (Schulz & Struck 2001), potentially leading to gas be- ing deposited into the galaxy centre. Additional processes such as frequent high-speed galaxy encounters (galaxy harassment; Moore et al. 1996) and tidal interactions between the galaxy and the cluster potential (Byrd & Valtonen 1990) may also induce gas flows to the centre of a galaxy, triggering AGN.
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AGN Photoionization of Gas in Companion Galaxies as a Probe of AGN Radiation in Time and Direction

AGN Photoionization of Gas in Companion Galaxies as a Probe of AGN Radiation in Time and Direction

UGC 6081: This pair has two heavily reddened Sy 2 nuclei and shows AGN ionization along an extent of 58 arcsec (41 kpc). The extended emission might fall in the same category of radial extent >10 kpc as the ‘Voorwerpjes’ (Keel et al. 2012a), depending on which of the AGN lights it up. We do not have the three-dimensional information to tell which is responsible (if indeed one dominates in the tidal debris seen at large radii). We do have the information for a rough ionization-balance calculation as done above for NGC 5278/9. These nuclei are more luminous and much more heavily reddened than in NGC 5278/9; applying a single foreground-screen reddening correction based on the nuclear Balmer decrements sug- gests that the NW AGN, in the smaller galaxy (UGC 6081 NED01), is twice as luminous in [O III ]. Our estimates (Table 4, listing dered- dened values in this system) show that the energy balance makes it plausible for the SE AGN (in UGC 6081 NED02) to power the most distant gas we observe spectroscopically along the slit to its south- east, although whether this works in detail depends critically on the fne structure of the gas (since the peak surface brightness we ob- serve places the strongest limits on the incident fux, and is strongly dependent on image quality). Much of the reddening toward each nucleus may take place close to our line of sight rather than as surrounding ‘cocoons’ covering large solid angles; the WISE data suggest that in neither one does the MIR component of the SED dominate over ionizing radiation reaching surrounding gas. Using our conservative fne-structure correction (a factor of 3 as noted above), the case for AGN fading in this system is weak (energy shortfall 1.7–2.0 times depending on which AGN is responsible, and no shortfall if both contribute to the ionization of the extended cloud).
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The Brightest z ≳ 8 Galaxies over the COSMOS UltraVISTA Field

The Brightest z ≳ 8 Galaxies over the COSMOS UltraVISTA Field

tral features (e.g., Stark et al. 2015a,b, 2017) and im- prove estimates of stellar mass and star formation rate. However, spectroscopic confirmation has been very chal- lenging so far, with fewer than expected (e.g., Stark et al. 2011) normal galaxies with robust redshift mea- surements at z > 7 (e.g., Vanzella et al. 2011; Pentericci et al. 2011; Ono et al. 2012; Schenker et al. 2012; Shibuya et al. 2012; Finkelstein et al. 2013; Tilvi et al. 2014; Song et al. 2016; Schmidt et al. 2016; Huang et al. 2016; Hoag et al. 2017, 2018; Larson et al. 2018; Pentericci et al. 2018). The likely reason for this is the increased neutral fraction at z & 6 combined with the faintness of the sources (e.g., Treu et al. 2013; Schenker et al. 2014; Pentericci et al. 2014; Tilvi et al. 2014). Interest- ingly, a number of recent works have reported spectro- scopic confirmation for bright (H ∼ 25 mag) LBGs at the epoch of the reionization from Lyα detection (Oesch et al. 2015b; Roberts-Borsani et al. 2016; Stark 2016; Zitrin et al. 2015). These observations further suggested that reionization could have happened in a patchy form, rather than homogeneously, and inspired confidence in our ability to reliably select bright sources to the highest possible redshifts.
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Galaxy and Mass Assembly (GAMA): active galactic nuclei in pairs of galaxies

Galaxy and Mass Assembly (GAMA): active galactic nuclei in pairs of galaxies

We compare the u − r colours of the neighbouring inactive (in a nuclear sense) galaxies of T1, extended T1 and T2 AGN in pairs. The u − r colours are taken from the GAMA stellar mass cata- logue (S tellar M assesv 18; Taylor et al. 2011) and are taken from the modelled AB rest-frame SDSS u and r bands. These magni- tudes are extinction and k-corrected. The distributions of the u − r when the neighbours of AGN of all [O III](5007Å) luminosities are considered appear to similar between AGN type (see Figure 10). To statistically assess this apparent similarity we perform a KS test on the colour distributions of the neighbours of T2 and ex- tended catalogue T1s to maximise the numbers of galaxies used in this analysis. We find that the probability that the colour distri- bution of the neighbouring galaxies of T1-extended and T2 AGN are drawn from the same parent population to be greater than 11%, with a p-value of 0.117. That is to say we cannot confidently say the distributions are drawn from different parent populations. This result doesn’t change if the subset of neighbours of bona fide T1s
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School Desegregation, Law and Order, and Litigating Social Justice in Alabama, 1954 1973

School Desegregation, Law and Order, and Litigating Social Justice in Alabama, 1954 1973

This dissertation incorporates optical photometry & photopolarimetry along with gamma-ray data from the Fermi/LAT instrument in order to conduct a survey of these properties for a sample of RL NLS1 galaxies. This sample was derived from lists of RL NLS1s presented in Yuan et al. (2008), Komossa et al. (2006), Whalen et al. (2006), and Calderone et al. (2012). The determination of the NLS1 natures of these objects was accomplished primarily via the use of SDSS spectroscopy, while the radio-loudness was determined by using data from radio surveys, such as the FIRST survey (Becker et al., 1995). The specific objects chosen for this study were selected based on thier location on the sky (between -30º < Dec. < 60º, due to hardware limits for the telescopes at Lowell Observatory) and optical brightness in the R-band (i.e. brighter than R ⇡ 20, which is close to the effective magnitude limit of the 72-inch Perkins telescope). The majority, if not all, of the activity in the regimes mentioned above for blazars is believed to originate in relativistic jets oriented close to the line of sight of the observer. By selecting these observational regimes, this work proposes to both survey these properties for a sample of RL NLS1 objects and to interpret the results in light of the physical mechanisms governing relativistic jets, as described above. The purpose of such a survey will be, ultimately, to characterize the RL NLS1 galaxies in the context of key blazar properties.
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The core flux of the brightest 10 μm galaxies in the southern sky

The core flux of the brightest 10 μm galaxies in the southern sky

Since the operation of MIDI at the VLTI began in 2004, astron- omy has entered a new era where it is now possible to reach a resolution of a few milliarcseconds at infrared wavelengths, about 15 times the resolution of the largest single-dish tele- scopes. MIDI operates in the N-band (8−13 µm) and therefore it is ideal for observing heated dust expected in AGNs and star- burst galaxies. Although it is most commonly used in observ- ing galactic objects like circumstellar disks (Leinert et al. 2004) and dust shells around evolved stars (Ohnaka et al. 2005), MIDI has been successfully used to observe extragalactic objects. The main limitation of MIDI in this context is its limiting flux of ∼400 mJy, so only bright objects can be observed currently. So far, MIDI has been used to observe dusty tori in AGNs, objects which are central to the AGN unification model, and which have proven too small to be resolved by a single dish telescope. With its superior resolution, the presence of a torus-like structure has been established in the galaxy NGC 1068 (Jaffe et al. 2004) by using only two baseline observations, and additional MIDI ob- servations with extensive coverage of up to 21 baselines have measured the geometrical properties of the torus in the Circinus galaxy (Tristram et al. 2007) and NGC 1068 (Raban et al., sub- mitted). A resolved dust structure was also detected in the core of Centaurus A (Meisenheimer et al. 2007). Apart from active galactic nuclei, the only extragalactic objects bright enough for
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VLT spectroscopy of the z=4.11 Radio Galaxy TN J1338-1942

VLT spectroscopy of the z=4.11 Radio Galaxy TN J1338-1942

Although, with only two measurements, the statistical sig- nificance of the low radio galaxy D A values is marginal, the result is suggestive. It is worthwhile contemplating the impli- cations that would follow if further observations of z > 4 radio galaxies and other objects selected without an optical color bias confirmed this trend. Given that optical color selection methods (often used to find quasars, and Lyman break galaxies) favour objects with large D A values, it is perhaps not surprising that non-color selected z > 4 objects might have lower values of D A . Consequently, quasars and galaxies with low D A values might be missed in color–based surveys. This then could lead to an underestimate of their space densities, and an overestimate of the average H i columns density through the universe.
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A Tale of Two Clusters: An Analysis of Gas-phase Metallicity and Nebular Gas Conditions in Proto-cluster Galaxies at z < 2

A Tale of Two Clusters: An Analysis of Gas-phase Metallicity and Nebular Gas Conditions in Proto-cluster Galaxies at z < 2

galaxy metallicity and directly compare two proto-clusters at z ∼ 2 to the field. Gas-phase metallicity values for the same galaxy can differ between metallicity indicators by up to 1 order of magnitude (Kewley & Ellison 2008). Discrep- ancies between different strong-line indicators are possibly the result of calibration on local HII regions, which depend on the measurement of electron temperature (Pilyugin & Thuan 2005; Pilyugin & Mattsson 2011; Maiolino & Man- nucci 2019). Calibrations using local HII re- gions can be flawed when used for high-redshift measurements because possible changes in the nebular gas properties of high-redshift galaxies have been observed compared to local galax- ies. In particular, galaxies at high redshift have been observed to have higher ionization param- eter and electron density than local galaxies (Brinchmann et al. 2008; Liu et al. 2008; Lehn- ert et al. 2009; Newman et al. 2012; Kewley et al. 2013; Tacconi et al. 2013; Newman et al. 2014; Shirazi et al. 2014; Steidel et al. 2014; Shapley et al. 2015; Steidel et al. 2016; Kaasi- nen et al. 2018; Harshan et al. in prep).
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