Evidence that the z = 3.4 radio galaxy B2 0902+34 may be a protogalaxy
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Protogalaxy
X-shaped radio galaxy
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Context. X-shaped radio galaxies (XRGs) exhibit a pair of bright primary lobes and a pair of weak secondary lobes (wings), which are oriented with an angle that gives the structure a cross-like shape. Though several theoretical models have been proposed to explain their origin, there is currently not a general consensus on a formation scenario. Aims. We analysed new multifrequency Karl G. Jansky Very Large Array (JVLA) radio data at 1.5, 5.5, 6, and 9 GHz of the candidate XRG in Abell 3670 (A3670) in order to characterise and classify it for the first time and to investigate its origin. Methods. We produced flux, spectral index, and radiative age maps of A3670 by means of the new radio data. We investigated the connection between the radio galaxy and its host, a brightest cluster galaxy (BCG) with two optical nuclei classified as a dumbbell galaxy. Finally we discussed the literature models and compared them to the observed properties of A3670. Results. We classify A3670 as a Fanaroff-Riley I-type XRG and measured a 1.4 GHz radio power of 1.7 x 10^25 W Hz-1. By estimating the radiative age of the various source components, we find that the wings are 20 Myr older than the lobes. We verified that the lobes and wings are aligned with the major and minor axes of the optical galaxy, respectively, and we estimated a black hole mass of 10^9 Msun , which is in agreement with the typical properties of the XRGs. Conclusions. Among the discussed scenarios, the jet-shell interaction model may best reproduce the observed properties of A3670. The gas of a stellar shell is responsible for the deflection of the jets, thus forming the wings. The presence of stellar shells in A3670 is plausible, but it needs further optical observations to be confirmed.
X-shaped radio galaxy
Jansky
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A sensitive observation of the CO J = 1-0 molecular line emission in the host galaxy of GRB 030329 (z = 0.1685) has been performed using the Nobeyama Millimeter Array to detect molecular gas and hidden star formation. No sign of CO emission was found, which invalidates our previous report of the presence of molecular gas. The 3 σ upper limit on the CO line luminosity (L) of the host galaxy is 6.9 × 108 K km s-1 pc2. The lower limit to the host galaxy's metallicity is estimated to be 12 + log (O/H) ~ 7.9, which yields a conversion factor from CO line luminosity to H2 of αCO = 40 M☉ (K km s-1 pc2)-1. Assuming this factor, the 3 σ upper limit on the molecular gas mass of the host galaxy is 2.8 × 1010 M☉. Based on the Schmidt law, the 3 σ upper limit on the total star formation rate (SFR) of the host galaxy is estimated to be 38 M☉ yr-1. These results independently confirm inferences from previous observations in the optical, submillimeter, and X-ray bands, which regard this host galaxy as a compact dwarf and not a massive, aggressively star-forming galaxy. Finally, the SFRs of GRB host galaxies, estimated using various techniques immune to dust obscuration, including our CO luminosity measurements, are compared with the SFRs of the same galaxies estimated using extinction-corrected optical/UV tracers. We show that most of the SFRs measured in extinction-free wavelengths, including positive detections and upper limits, are larger by from 1 to a few orders of magnitude compared with the SFRs of the same galaxies measured by optical/UV tracers.
Extinction (optical mineralogy)
Submillimeter Array
Irregular galaxy
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Observations from the HERschel Inventory of the Agents of Galaxy Evolution (HERITAGE) have been used to identify dusty populations of sources in the Large and Small Magellanic Clouds (LMC and SMC). We conducted the study using the HERITAGE catalogs of point sources available from the Herschel Science Center from both the Photodetector Array Camera and Spectrometer (PACS; 100 and 160 μm) and Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, and 500 μm) cameras. These catalogs are matched to each other to create a Herschel band-merged catalog and then further matched to archival Spitzer IRAC and MIPS catalogs from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and SAGE-SMC surveys to create single mid- to far-infrared (far-IR) point source catalogs that span the wavelength range from 3.6 to 500 μm. There are 35,322 unique sources in the LMC and 7503 in the SMC. To be bright in the FIR, a source must be very dusty, and so the sources in the HERITAGE catalogs represent the dustiest populations of sources. The brightest HERITAGE sources are dominated by young stellar objects (YSOs), and the dimmest by background galaxies. We identify the sources most likely to be background galaxies by first considering their morphology (distant galaxies are point-like at the resolution of Herschel) and then comparing the flux distribution to that of the Herschel Astrophysical Terahertz Large Area Survey (ATLAS) survey of galaxies. We find a total of 9745 background galaxy candidates in the LMC HERITAGE images and 5111 in the SMC images, in agreement with the number predicted by extrapolating from the ATLAS flux distribution. The majority of the Magellanic Cloud-residing sources are either very young, embedded forming stars or dusty clumps of the interstellar medium. Using the presence of 24 μm emission as a tracer of star formation, we identify 3518 YSO candidates in the LMC and 663 in the SMC. There are far fewer far-IR bright YSOs in the SMC than the LMC due to both the SMC's smaller size and its lower dust content. The YSO candidate lists may be contaminated at low flux levels by background galaxies, and so we differentiate between sources with a high ("probable") and moderate ("possible") likelihood of being a YSO. There are 2493/425 probable YSO candidates in the LMC/SMC. Approximately 73% of the Herschel YSO candidates are newly identified in the LMC, and 35% in the SMC. We further identify a small population of dusty objects in the late stages of stellar evolution including extreme and post-asymptotic giant branch, planetary nebulae, and supernova remnants. These populations are identified by matching the HERITAGE catalogs to lists of previously identified objects in the literature. Approximately half of the LMC sources and one quarter of the SMC sources are too faint to obtain accurate ample FIR photometry and are unclassified.
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Point source
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We explore the internal dynamics of Abell 2254, which has been shown to host a very clumpy and irregular radio halo. Our analysis is mainly based on redshift data for 128 galaxies acquired at the TNG. We also use new g',r',i' photometric data acquired at the INT and (V,i') photometric data available in the Subaru Archive. X-ray data from the XMM-Newton Science Archive are analyzed to study the hot gas component. We estimate the cluster redshift =0.177, a high line-of-sight (LOS) velocity dispersion, sigmaV about 1350 km/s, and X-ray temperature T about 6.4 keV. Both our optical and X-ray analyses reveal a complex dynamical activity. The analysis of the 2D galaxy distribution reveals the presence of two density peaks, one at the East and the other at the West. Using the full 3D information we detect a high LOS velocity (DeltaV about 3000 km/s), low mass group at the position of the 2D eastern peak. For the main system we compute a velocity dispersion sigmaV about 1000-1200 km/s. In the assumption of a bimodal system we estimate a mass M=1.5-2.9 10^15 solar masses.The X-ray morphological analysis confirms that Abell 2254 is a dynamically disturbed cluster. The X-ray isophotes are elongated toward the eastern direction, in agreement with a merger in the post core-crossing phase. A simple bimodal model finds that data are consistent with a bound, outgoing subcluster observed a few fractions of Gyr after the core crossing. However, both optical and X-ray analyses suggest that the main system is, at its time, a non relaxed structure, indicating N-S as a possible direction for a past accretion. We conclude that Abell 2254, for its mass and merging structure, fits well among typical clusters with radio halos. We shortly discuss as the particular irregularity of the radio halo might be linked to the complexity of the Abell 2254 structure.
X-shaped radio galaxy
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The protogalaxy cB58 was discovered in the Canadian Network of Observational Cosmology (CNOC) survey of cluster redshifts. Absorption features reveal that this system is at a redshift of z = 2.72, implying an absolute magnitude of Mv ∼− 26, and has a star formation rate of 4700 M⊙ yr−1, making it the most ‘active’ star-forming galaxy. This protogalaxy is observed to lie close ( ∼ 6 arcsec) to a central cluster galaxy at z = 0.373. The X-ray properties of the cluster suggest that its mass, and therefore its lensing potential, could be greater than that found using a virial analysis. In this Letter we argue that the phenomenal properties of this protogalaxy are due to the gravitational lensing effect of the foreground cluster, and the unlensed properties of the source are typical of high-redshift star-forming systems.
Protogalaxy
Virial mass
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Explaining the existence of $\gtrsim10^8\,\mathrm{M_\odot}$ SMBHs at $z>6$ is a persistent challenge to modern astrophysics. Multi-wavelength observations of $z\gtrsim6$ QSOs reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray (XMM-Newton, 100 ks) follow-up observations of a $z\approx6$ QSO, J1641+3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641+3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor $\gtrsim7$ on a notably short timescale (i.e., $\approx115$ rest-frame days), making it the $z>4$ QSO with the largest variability amplitude. We also obtained rest-frame UV spectroscopic and photometric data with textit{LBT}, and compared them with archival datasets. Surprisingly, we found that J1641+3755 became brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Multiple narrow absorption features are detected in its rest-frame UV spectrum, and several of them can be associated with an intervening system at $z=5.67$. The variability properties of J1641+3755 can be due to intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, or an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the $z>6$ QSOs with multiple X-ray observations separated by $>10$ rest-frame days, we found an enhancement of strongly (i.e., by a factor $>3$) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift QSOs.
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Protogalaxy
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The bright, soft X-ray spectrum Seyfert 1 galaxies Ark 564 and Ton S180 were monitored for 35 days and 12 days, respectively, with ASCA and RXTE (and EUVE for Ton S180). These represent the most intensive X-ray monitoring of any such soft-spectrum Seyfert 1 to date. Light curves were constructed for Ton S180 in six bands spanning 0.1-10 keV and for Ark 564 in five bands spanning 0.7-10 keV. The short-timescale (hours-days) variability patterns were very similar across energy bands, with no evidence of lags between any of the energy bands studied. The fractional variability amplitude was almost independent of energy band, unlike hard-spectrum Seyfert 1 galaxies, which show stronger variations in the softer bands. It is difficult to simultaneously explain soft Seyfert galaxies stronger variability, softer spectra, and weaker energy dependence of the variability relative to hard Seyfert galaxies. There was a trend for soft- and hard-band light curves of both objects to diverge on the longest timescales probed (~weeks), with the hardness ratio showing a secular change throughout the observations. This is consistent with the fluctuation power density spectra that showed relatively greater power on long timescales in the softest bands. The simplest explanation of all of these is that two continuum emission components are visible in the X-rays: a relatively hard, rapidly variable component that dominates the total spectrum and a slowly variable soft excess that only shows up in the lowest energy channels of ASCA. Although it would be natural to identify the latter component with an accretion disk and the former with a corona surrounding it, a standard thin disk could not get hot enough to radiate significantly in the ASCA band, and the observed variability timescales are much too short. It also appears that the hard component may have a more complex shape than a pure power law. The most rapid factor of 2 flares and dips occurred within ~1000 s, in Ark 564 and a bit more slowly in Ton S180. The speed of the luminosity changes rules out viscous or thermal processes and limits the size of the individual emission regions to ≲15 Schwarzschild radii (and probably much less), that is, to either the inner disk or small regions in a corona.
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