We present MUSE observations of AM1354-250, confirming its status as a collisional ring galaxy which has recently undergone an interaction, creating its distinctive shape. We analyse the stellar and gaseous emission throughout the galaxy finding direct evidence that the gaseous ring is expanding with a velocity of $\sim$70km.s$^{-1}$ and that star formation is occurring primarily in HII regions associated with the ring. This star formation activity is likely triggered by the interaction. We find evidence for several excitation mechanisms in the gas, including emission consistent with shocked gas in the expanding ring and a region of LINER-like emission in the central core of the galaxy. Evidence of kinematic disturbance in both the stars and gas, possibly also triggered by the interaction, can be seen in all of the velocity maps. The ring galaxy retains weak spiral structure, strongly suggesting the progenitor galaxy was a massive spiral prior to the collision with its companion an estimated $140 \pm 12$ Myr ago.
In this letter, we checked spectral properties of the well-known narrow line Seyfert I Mrk142, in order to try to find effects of narrow line variability on BLR radius of Mrk142 which is an outlier in the R-L plane. Although, no improvement can be found on BLR radius, apparent narrow line variability can be confirmed in Mrk142. Using the public spectra collected from the Lick AGN Monitoring Project, the spectral scaling method based on assumption of constant \oiii line is firstly checked by examining broad and narrow emission line properties. We find that with the application of the spectral scaling method, there is a strong correlation between the \oiii line flux and the \oiii line width, but weaker correlations between the broad H$\alpha$ flux and the broad H$\beta$ flux, and between the broad H$\alpha$ flux and the continuum emission at 5100\AA. The results indicate that the assumption of constant \oiii line is not preferred, and caution should be exercised when applying the spectral scaling calibration method. And then, we can find a strong correlation between the \oiii line flux and the continuum emission at 5100\AA, which indicates apparent short-term variability of the \oiii line in Mrk142 over about two months.
We have selected a sample of 80 candidates for obscured radio-loud active galactic nuclei and presented their basic optical/near-infrared (NIR) properties in Paper 1. In this paper, we present both high-resolution radio continuum images for all of these sources and HI 21cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz VLA continuum observations find that 52 sources are compact or have substantial compact components with size <0.5" and flux density >0.1 Jy at 4.9 GHz. The most compact 36 sources were then observed with the VLBA at 1.4 GHz. One definite and 10 candidate Compact Symmetric Objects (CSOs) are newly identified, a detection rate of CSOs ~3 times higher than the detection rate previously found in purely flux-limited samples. Based on possessing compact components with high flux densities, 60 of these sources are good candidates for absorption-line searches. Twenty seven sources were observed for HI 21cm absorption at their photometric or spectroscopic redshifts with only 6 detections made (one detection is tentative). However, five of these were from a small subset of six CSOs with pure galaxy optical/NIR spectra and for which accurate spectroscopic redshifts place the redshifted 21cm line in a RFI-free spectral window. It is likely that the presence of ubiquitous RFI and the absence of accurate spectroscopic redshifts preclude HI detections in similar sources (only one detection out of the remaining 22 sources observed, 14 of which have only photometric redshifts). Future searches for highly-redshifted HI and molecular absorption can easily find more distant CSOs among bright, blank field' radio sources but will be severely hampered by an inability to determine accurate spectroscopic redshifts for them due to their lack of rest-frame UV continuum.
Gamma-ray bursts allow us to pinpoint and study star-forming galaxies in the early universe, thanks to their immense luminosities and association with deaths of massive stars. We present {\em Hubble Space Telescope} Wide Field Camera 3 detections of three {\em Swift} GRBs lying at redshifts $z = 5.913$ (GRB 130606A), $z = 6.295$ (GRB 050904), and $z = 6.327$ (GRB 140515A) in the F140W (wide-$JH$ band, $\lambda_{\rm{obs}}\sim1.4\,\mu m$) filter. The hosts have magnitudes (corrected for Galactic extinction) of $m_{\rm{\lambda_{obs},AB}}= 26.26^{+0.12}_{-0.14}, 27.63^{+0.16}_{-0.18},$ and $28.23^{+0.24}_{-0.30}$ respectively. In all three cases the probability of chance coincidence of lower redshift galaxies is $\lesssim1.5\%$, indicating that the detected galaxies are most likely the GRB hosts. These are the first detections of high redshift ($z > 5$) GRB host galaxies in emission. The galaxies have luminosities in the range $0.1-0.7\,L^{*}_{z=6}$ (with $M_{1600}^{*}=-20.95\pm0.12$), along with half-light radii in the range $0.6-1.2\,\rm{kpc}$. Both their half-light radii and luminosities are consistent with existing samples of Lyman-break galaxies at $z\sim6$. Spectroscopic analysis of the GRB afterglows indicate low metallicities ($[\rm{M/H}]\lesssim-1$) and dust extinction ($A_{\rm{V}}\lesssim0.1$) along the line of sight. We consider the implications of these luminosities for their possible star formation histories and the potential for emission line metallicity determinations with {\em James Webb Space Telescope} spectroscopy.
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Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum.
We consider stars with radial velocities, proper motions, and distance
estimates from the RAVE4 catalogue. Based on a sample of more than 145000 stars
at distances $r<0.5$~kpc, we have found the following kinematic parameters:
(U,V,W)_\odot=(9.12, 20.80, 7.66)\pm(0.10, 0.10, 0.08) km s^{-1},
\Omega_0=28.71\pm0.63 km s^{-1} kpc^{-1}, and
\Omega'_0=-4.28\pm0.11 km s^{-1} kpc^{-2}. This gives the linear rotation
velocity V_0=230\pm12 km s^{-1} (for the adopted R_0= 8.0\pm0.4 kpc) and the
Oort constants A=17.12\pm0.45 km s^{-1} kpc^{-1} and B=-11.60\pm0.77 km s^{-1}
kpc^{-1}. The 2D velocity distributions in the UV, UW, and VW planes have been
constructed using a local sample, r<0.25 kpc, consisting of \sim 47000 stars. A
difference of the UV velocity distribution from the previously known ones
constructed from a smaller amount of data has been revealed. It lies in the
fact that our distribution has an extremely enhanced branch near the Wolf 630
peak. A previously unknown peak at (U,V)=(-96,-10) km s^{-1} and a separate new
feature in the Wolf 630 stream, with the coordinates of its center being
(U,V)=(30,-40) km s^{-1}, have been detected.
The origin and evolution of cosmic magnetic fields as well as the influence of the magnetic fields on the evolution of galaxies are unknown. Though not without challenges, the dynamo theory can explain the large-scale coherent magnetic fields which govern galaxies, but observational evidence for the theory is so far very scarce. Putting together the available data of non-interacting, non-cluster galaxies with known large-scale magnetic fields, we find a tight correlation between the integrated polarized flux density and the rotation speed, v(rot), of galaxies. This leads to an almost linear correlation between the large-scale magnetic field B and v(rot), assuming that the number of cosmic ray electrons is proportional to the star formation rate. This correlation cannot be attributed to an active linear dynamo processes, as no correlation holds with shear or angular speed. It indicates instead a coupling between the large-scale magnetic field and the dynamical mass of the galaxies, B~M(dyn)^{0.2-0.3}. Hence, faster rotating and/or more massive galaxies have stronger large-scale magnetic fields. The observed B-v(rot) correlation shows that the anisotropic turbulent magnetic field dominates B in fast rotating galaxies as the turbulent magnetic field, coupled with gas, is enhanced and ordered due to the strong gas compression and/or shear in these systems. This study supports a stationary condition and no further evolution of the large-scale magnetic field as long as the dynamical mass of galaxies is constant.
We present the $^{13}$CO/C$^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The high-resolution spectral survey currently covers |b| < 0.5 deg and 28 < l < 46 deg, with an angular resolution of 15 arcsec in 0.5 km/s velocity channels. The spectra have a median rms of $\sim$ 0.6 K at this resolution, and for optically thin gas at an excitation temperature of 10 K, this sensitivity corresponds to column densities of $N_{\mathrm{H}_{2}} \sim 3 \times 10^{20}\,$cm$^{-2}$ and $N_{\mathrm{H}_{2}} \sim 4 \times 10^{21}\,$cm$^{-2}$ for $^{13}$CO and C$^{18}$O, respectively. The molecular gas that CHIMPS traces is at higher column densities and is also more optically thin than in other publicly available CO surveys due to its rarer isotopologues, and thus more representative of the three-dimensional structure of the clouds. The critical density of the J=3-2 transition of CO is $\gtrsim 10^{4}$ cm$^{-3}$ at temperatures of $\leq 20$ K, and so the higher density gas associated with star formation is well traced. These data complement other existing Galactic plane surveys, especially the JCMT Galactic Plane Survey which has similar spatial resolution and column density sensitivity, and the Herschel infrared Galactic Plane Survey. In this paper, we discuss the observations, data reduction and characteristics of the survey, presenting integrated emission maps for the region covered. Position-velocity diagrams allow comparison with Galactic structure models of the Milky Way, and while we find good agreement with a particular four arm model, there are some significant deviations.
We derive a free-form mass distribution for the massive cluster AS1063 (z=0.348) using the completed optical imaging from the Hubble Frontier Fields programme. Based on a subset of 11 multiply lensed systems with spectroscopic redshift we produce a lens model that is accurate enough to unveil new multiply lensed systems, totalling over a 100 arclets, and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using only the subset of lensed sources with spectroscopically measured redshifts. No significant offset is found between the centroid of our mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster, although a relatively large elongation of the mass distribution is apparent relative to the X-ray map. For the well resolved lensed images we provide detailed model comparisons to illustrate the precision of our model and hence the reliability of our de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example of jet-induced star formation, at redshift z=3.1.
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Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum.
We consider stars with radial velocities, proper motions, and distance
estimates from the RAVE4 catalogue. Based on a sample of more than 145000 stars
at distances $r<0.5$~kpc, we have found the following kinematic parameters:
(U,V,W)_\odot=(9.12, 20.80, 7.66)\pm(0.10, 0.10, 0.08) km s^{-1},
\Omega_0=28.71\pm0.63 km s^{-1} kpc^{-1}, and
\Omega'_0=-4.28\pm0.11 km s^{-1} kpc^{-2}. This gives the linear rotation
velocity V_0=230\pm12 km s^{-1} (for the adopted R_0= 8.0\pm0.4 kpc) and the
Oort constants A=17.12\pm0.45 km s^{-1} kpc^{-1} and B=-11.60\pm0.77 km s^{-1}
kpc^{-1}. The 2D velocity distributions in the UV, UW, and VW planes have been
constructed using a local sample, r<0.25 kpc, consisting of \sim 47000 stars. A
difference of the UV velocity distribution from the previously known ones
constructed from a smaller amount of data has been revealed. It lies in the
fact that our distribution has an extremely enhanced branch near the Wolf 630
peak. A previously unknown peak at (U,V)=(-96,-10) km s^{-1} and a separate new
feature in the Wolf 630 stream, with the coordinates of its center being
(U,V)=(30,-40) km s^{-1}, have been detected.
The origin and evolution of cosmic magnetic fields as well as the influence of the magnetic fields on the evolution of galaxies are unknown. Though not without challenges, the dynamo theory can explain the large-scale coherent magnetic fields which govern galaxies, but observational evidence for the theory is so far very scarce. Putting together the available data of non-interacting, non-cluster galaxies with known large-scale magnetic fields, we find a tight correlation between the integrated polarized flux density and the rotation speed, v(rot), of galaxies. This leads to an almost linear correlation between the large-scale magnetic field B and v(rot), assuming that the number of cosmic ray electrons is proportional to the star formation rate. This correlation cannot be attributed to an active linear dynamo processes, as no correlation holds with shear or angular speed. It indicates instead a coupling between the large-scale magnetic field and the dynamical mass of the galaxies, B~M(dyn)^{0.2-0.3}. Hence, faster rotating and/or more massive galaxies have stronger large-scale magnetic fields. The observed B-v(rot) correlation shows that the anisotropic turbulent magnetic field dominates B in fast rotating galaxies as the turbulent magnetic field, coupled with gas, is enhanced and ordered due to the strong gas compression and/or shear in these systems. This study supports a stationary condition and no further evolution of the large-scale magnetic field as long as the dynamical mass of galaxies is constant.
We present the $^{13}$CO/C$^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The high-resolution spectral survey currently covers |b| < 0.5 deg and 28 < l < 46 deg, with an angular resolution of 15 arcsec in 0.5 km/s velocity channels. The spectra have a median rms of $\sim$ 0.6 K at this resolution, and for optically thin gas at an excitation temperature of 10 K, this sensitivity corresponds to column densities of $N_{\mathrm{H}_{2}} \sim 3 \times 10^{20}\,$cm$^{-2}$ and $N_{\mathrm{H}_{2}} \sim 4 \times 10^{21}\,$cm$^{-2}$ for $^{13}$CO and C$^{18}$O, respectively. The molecular gas that CHIMPS traces is at higher column densities and is also more optically thin than in other publicly available CO surveys due to its rarer isotopologues, and thus more representative of the three-dimensional structure of the clouds. The critical density of the J=3-2 transition of CO is $\gtrsim 10^{4}$ cm$^{-3}$ at temperatures of $\leq 20$ K, and so the higher density gas associated with star formation is well traced. These data complement other existing Galactic plane surveys, especially the JCMT Galactic Plane Survey which has similar spatial resolution and column density sensitivity, and the Herschel infrared Galactic Plane Survey. In this paper, we discuss the observations, data reduction and characteristics of the survey, presenting integrated emission maps for the region covered. Position-velocity diagrams allow comparison with Galactic structure models of the Milky Way, and while we find good agreement with a particular four arm model, there are some significant deviations.
We derive a free-form mass distribution for the massive cluster AS1063 (z=0.348) using the completed optical imaging from the Hubble Frontier Fields programme. Based on a subset of 11 multiply lensed systems with spectroscopic redshift we produce a lens model that is accurate enough to unveil new multiply lensed systems, totalling over a 100 arclets, and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using only the subset of lensed sources with spectroscopically measured redshifts. No significant offset is found between the centroid of our mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster, although a relatively large elongation of the mass distribution is apparent relative to the X-ray map. For the well resolved lensed images we provide detailed model comparisons to illustrate the precision of our model and hence the reliability of our de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example of jet-induced star formation, at redshift z=3.1.
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We investigate the spatial distribution of satellite galaxies that were obtained from a mock redshift survey of the first Millennium Run simulation. The satellites were identified using typical redshift space criteria and, hence, the sample includes both genuine satellites and a large number of interlopers. As expected from previous work, the 3D locations of the satellites are well-fitted by a combination of a Navarro, Frenk & White (NFW) density profile and a power law. At fixed stellar mass, the NFW scale parameter, r_s, for the satellite distribution of red hosts exceeds that for the satellite distribution of blue hosts. In both cases the dependence of r_s on host stellar mass is well-fitted by a power law. For the satellites of red hosts, r_s^{red} \propto (M_\ast / M_sun)^{0.71 \pm 0.05} while for the satellites of blue hosts, r_s^{blue} \propto (M_\ast / M_sun)^{0.48 \pm 0.07}. For hosts with stellar masses greater than 4.0E+10 M_sun, the satellite distribution around blue hosts is much more concentrated than it is around red hosts with the same stellar mass. We perform model fits to the projected (2D) locations of the satellites and find that, with the exception of the satellites of the most massive red hosts, the 2D analysis accurately recovers the values of r_s obtained from the 3D analysis. Therefore, even in the limit of a large number of interlopers, the 3D distribution can be recovered using 2D information alone. The spatial distribution of the satellites of red hosts traces that of the hosts' halos; however, the spatial distribution of the satellites of blue hosts is more concentrated that of the hosts' halos by a factor of ~2. This calls into question whether observed satellites that are selected from redshift space can be used to directly infer the concentration of the dark matter halos of massive, blue host galaxies in our universe.
The black hole in the center of the Galaxy, associated with the compact source Sagittarius A* (Sgr A*), is predicted to cast a shadow upon the emission of the surrounding plasma flow, which encodes the influence of general relativity in the strong-field regime. The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) network with a goal of imaging nearby supermassive black holes (in particular Sgr A* and M87) with angular resolution sufficient to observe strong gravity effects near the event horizon. General relativistic magnetohydrodynamic (GRMHD) simulations show that radio emission from Sgr A* exhibits vari- ability on timescales of minutes, much shorter than the duration of a typical VLBI imaging experiment, which usually takes several hours. A changing source structure during the observations, however, violates one of the basic assumptions needed for aperture synthesis in radio interferometry imaging to work. By simulating realistic EHT observations of a model movie of Sgr A*, we demonstrate that an image of the average quiescent emission, featuring the characteristic black hole shadow and photon ring predicted by general relativity, can nonetheless be obtained by observing over multiple days and subsequent processing of the visibilities (scaling, averaging, and smoothing) before imaging. Moreover, it is shown that this procedure can be combined with an existing method to mitigate the effects of interstellar scattering. Taken together, these techniques allow the black hole shadow in the Galactic center to be recovered on the reconstructed image.
Extreme coronal-line emitter (ECLE) SDSSJ095209.56+214313.3, known by its strong, fading, high ionization lines, has been a long standing candidate for a tidal disruption event, however a supernova origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: 1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and 2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-based Mercator telescope. The well-sampled, $\sim10$-year long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of $\pm5$ days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the \textsl{GALEX} data (early 2006) with the recently acquired Swift UVOT (June 2015) and Mercator observations (April 2015) demonstrate a decrease in the UV flux over a $\sim 10$ year period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors a SN origin. These new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that TDEs are in fact capable of powering the enigmatic class of ECLEs.
Because isolated high-velocity clouds (HVCs) are found at great distances from the Galactic radiation field and because they have subsolar metallicities, there have been no detections of dust in these structures. A key problem in this search is the removal of foreground dust emission. Using the Effelsberg-Bonn HI Survey and the Planck far-infrared data, we investigate a bright, cold, and clumpy HVC. This cloud apparently undergoes an interaction with the ambient medium and thus has great potential to form dust. To remove the local foreground dust emission we used a regularised, generalised linear model and we show the advantages of this approach with respect to other methods. To estimate the dust emissivity of the HVC, we set up a simple Bayesian model with mildly informative priors to perform the line fit instead of an ordinary linear least-squares approach. We find that the foreground can be modelled accurately and robustly with our approach and is limited mostly by the cosmic infrared background. Despite this improvement, we did not detect any significant dust emission from this promising HVC. The 3-sigma upper limit to the dust emissivity is an order of magnitude below the typical values for the Galactic interstellar medium.
We study the evolution of giant clumps in high-z disc galaxies using AMR cosmological simulations at redshifts z=6-1. Our sample consists of 34 galaxies, of halo masses 10^{11}-10^{12}M_s at z=2, run with and without radiation pressure (RP) feedback from young stars. While RP has little effect on the sizes and global stability of discs, it reduces the amount of star-forming gas by a factor of ~2, leading to a decrease in stellar mass by a similar factor by z~2. Both samples undergo violent disc instability (VDI) and form giant clumps of masses 10^7-10^9M_s at a similar rate, though RP significantly reduces the number of long-lived clumps. When RP is (not) included, clumps with circular velocity <40(20)km/s, baryonic surface density <200(100)M_s/pc^2 and baryonic mass <10^{8.2}(10^{7.3})M_s are short-lived, disrupted in a few free-fall times. The more massive and dense clumps survive and migrate toward the disc centre over a few disc orbital times. In the RP simulations, the distribution of clump masses and star-formation rates (SFRs) normalized to their host disc is very similar at all redshifts. They exhibit a truncated power-law with a slope slightly shallower than -2. Short-lived clumps preferentially have young stellar ages, low masses, high gas fractions and specific SFRs (sSFR), and they tend to populate the outer disc. The sSFR of massive, long-lived clumps declines with age as they migrate towards the disc centre, producing gradients in mass, stellar age, gas fraction, sSFR and metallicity that distinguish them from short-lived clumps. Ex situ mergers make up ~37% of the mass in clumps and ~29% of the SFR. They are more massive and with older stellar ages than the in situ clumps, especially near the disc edge. Roughly half the galaxies at redshifts z=4-1 are clumpy over a wide range of stellar mass, with clumps accounting for ~3-30% of the SFR but ~0.1-3% of the stellar mass.
We have considered the \textit{Fermi} $\gamma$-ray light curve of the blazar PKS 0537-441 during a high state extending from 2008/08/10 to 2011/08/27. The periodogram exhibits a peak at T $\sim$ 280 d, with a significance of $\sim$ 99.7 \%. A peak of similar relevance at $\frac{1}{2}$ T is found in the optical light curves. Considering the entire duration of the \textit{ Fermi} light curve 2008-2015, no significant peak is revealed, while the optical one remains meaningful. Comparing with recent observations of PKS 2155-304 and PG 1553+113 it seems that month-year oscillations can characterize some blazars. Month-scale oscillations can also show up only during phases of enhanced or bursting emission like in the case of PKS 0537-441.
We considered the regions of triggered star formation inside kpc-sized HI supershells in three dwarf galaxies: IC 1613, IC 2574 and Holmberg II. The ionized and neutral gas morphology and kinematics were studied based on our observations with scanning Fabry-Perot interferometer at the SAO RAS 6-m telescope and 21 cm archival data of THINGS and LITTLE THINGS surveys. The qualitative analysis of the observational data performed in order to highlight the two questions: why the star formation occurred very locally in the supershells, and how the ongoing star formation in HI supershells rims influence its evolution? During the investigation we discovered the phenomenon never observed before in galaxies IC 2574 and Holmberg II: we found faint giant (kpc-sized) ionized shells in H-alpha and [SII]6717,6731 lines inside the supergiant HI shells.
The high-ionization lines of the broad-line region (BLR) of thermal active galactic nuclei (AGNs) show blueshifts of a few hundred km/s to several thousand km/sec with respect to the low-ionization lines. This has long been thought to be due to the high-ionization lines of the BLR arising in a wind of which the far side of the outflow is blocked from our view by the accretion disc. Evidence for and against the disc-wind model is discussed. The biggest problem for the model is that velocity-resolved reverberation mapping repeatedly fails to show the expected kinematic signature of outflow of the BLR. The disc-wind model also cannot readily reproduce the red side of the line profiles of high-ionization lines. The rapidly falling density in an outflow makes it difficult to obtain high equivalent widths. We point out a number of major problems with associating the BLR with the outflows producing broad absorption lines. An explanation which avoids all these problems and satisfies the constraints of both the line profiles and velocity-resolved reverberation-mapping is a model in which the blueshifting is due to scattering off material spiraling inwards with an inflow velocity of half the velocity of the blueshifting. We discuss how recent reverberation mapping results are consistent with the scattering-plus-inflow model but do not support a disc-wind model. We propose that the anti-correlation of the apparent redshifting of H$\beta$ with the blueshifting of CIV is a consequence of contamination of the red wings of H$\beta$ by the broad wings of [O III].
We study the impact of photometric signal to noise on the accuracy of derived structural parameters of unresolved star clusters using MCMC model fitting techniques. Star cluster images were simulated as a smooth surface brightness distribution following a King profile convolved with a point spread function. The simulation grid was constructed by varying the levels of sky background and adjusting the cluster's flux to a specified signal to noise. Poisson noise was introduced to a set of cluster images with the same input parameters at each node of the grid. Model fitting was performed using emcee algorithm. The presented posterior distributions of the parameters illustrate their uncertainty and degeneracies as a function of signal to noise. By defining the photometric aperture containing 80% of the cluster's flux, we find that in all realistic sky background level conditions a signal to noise ratio of $\sim$50 is necessary to constrain the cluster's half-light radius to an accuracy better than $\sim$20%. The presented technique can be applied to synthetic images simulating various observations of extragalactic star clusters.
An accurate line list for calcium oxide is presented covering transitions between all bound ro-vibronic levels from the five lowest electronic states \X, \Ap, \A, \astate, and \bstate. The ro-vibronic energies and corresponding wavefunctionts were obtained by solving the fully coupled Schr\"{o}dinger equation. \textit{Ab initio} potential energy, spin-orbit, and electronic angular momentum curves were refined by fitting to the experimental frequencies and experimentally derived energies available in the literature. Using our refined model we could (i) reassign the vibronic states for a large portion of the experimentally derived energies [van Groenendael A., Tudorie M., Focsa C., Pinchemel B., Bernath P. F., 2005, J. Mol. Spectrosc., 234, 255], (ii) extended this list of energies to $J=79-118$ and (iii) suggest a new description of the resonances from the \A--\X\ system. We used high level \textit{ab initio} electric dipole moments reported previously [Khalil H., Brites V., Le Quere F., Leonard C., 2011, Chem. Phys., 386, 50] to compute the Einstein A coefficients. Our work is the first fully coupled description of this system. Our line list is the most complete catalogue of spectroscopic transitions available for $^{40}$Ca$^{16}$O and is applicable for temperatures up to at least 5000~K. CaO has yet to be observed astronomically but its transitions are characterised by being particularly strong which should facilitate its detection. The CaO line list is made available in an electronic form as supplementary data to this article and at \url{www.exomol.com}.
We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe), and we find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, we measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it would have an ejecta mass of 20+-5 solar masses. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex and <8.4 dex, respectively) near the explosion site.
To study star formation in low metallicity environments ([M/H] ~ -1 ,dex), we obtained deep near-infrared (NIR) images of Sh 2-207 (S207), which is an HII region in the outer Galaxy with spectroscopically determined metallicity of [O/H] ~= -0.8 dex. We identified a young cluster in the western region of S207 with a limiting magnitude of Ks =19.0 mag (10 sigma) that corresponds to a mass detection limit of <~0.1 M_sun and enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. From the fitting of the K-band luminosity function (KLF), the age and distance of S207 cluster are estimated at 2-3Myr and ~4 kpc, respectively. The estimated age is consistent with the suggestion of small extinctions of stars in the cluster (Av ~ 3 mag) and the non-detection of molecular clouds. The reasonably good fit between observed KLF and model KLF suggests that the underlying initial mass function (IMF) of the cluster down to the detection limit is not significantly different from the typical IMFs in the solar metallicity. From the fraction of stars with NIR excesses, a low disk fraction (<10 %) in the cluster with relatively young age is suggested, as we had previously proposed.
We briefly review some recent advances in the study of the shadows of rotating black holes in alternative theories. The size and the shape of the shadow depend on the mass and the angular momentum, and they can also depend on other parameters specific of the particular model adopted. As an example, we show the results corresponding to a rotating braneworld black hole.
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We investigate the structural properties of the underlying hosts of 34 blue compact dwarf (BCD) galaxies with deep near-infrared (NIR) photometry. The BCD sample is selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey in the Great observatories origins Deep Survey North and South fields. We extract the surface brightness profile (SBP) in the optical F 435W and NIR F 160W bands. The SBPs of BCDs in the H band reach 26 mag arcsec^-2 at the 3\sigma level, which is so far the deepest NIR imaging of BCDs. Then we fit the SBPs with one- and two- component Sersic models. About half of the BCDs favour the two-component model which significantly improves the fit quality. The effective radii of the underlying hosts of BCDs in the B band are smaller than those of early-type dwarfs (dEs) and dwarf irregulars at a fixed luminosity. This discrepancy is similar to findings in many previous works. However, the difference in structural parameters between BCDs and other dwarf galaxies seems to be less significant in the H band. Furthermore, we find a remarkable agreement between the underlying hosts of BCDs and dEs. All dwarf galaxies seem to follow a similar luminosity-radius relationship which suggests a unified structural evolution for dwarf galaxies. We conclude that a possible evolution track from BCDs to dEs cannot be ruled out, with no significant change of structure needed in the evolutionary scenario.
We revealed the detailed structure of a vastly extended H$\alpha$-emitting nebula ("H$\alpha$ nebula") surrounding the starburst/merging galaxy NGC 6240 by deep narrow-band imaging observations with the Subaru Suprime-Cam. The extent of the nebula is $\sim$90 kpc in diameter and the total H$\alpha$ luminosity amounts to $\approx 1.6 \times 10^{42}$ erg s$^{-1}$. The volume filling factor and the mass of the warm ionized gas are $\sim$10$^{-4}$--10$^{-5}$ and $\sim$$5 \times 10^8$ $M_\odot$, respectively. The nebula has a complicated structure, which includes numerous filaments, loops, bubbles, and knots. We found that there is a tight spatial correlation between the H$\alpha$ nebula and the extended soft X-ray-emitting gas, both in large and small scales. The overall morphology of the nebula is dominated by filamentary structures radially extending from the center of the galaxy. A large-scale bi-polar bubble extends along the minor axis of the main stellar disk. The morphology strongly suggests that the nebula was formed by intense outflows - superwinds - driven by starbursts. We also found three bright knots embedded in a looped filament of ionized gas that show head-tail morphologies in both emission-line and continuum, suggesting close interactions between the outflows and star forming regions. Based on the morphology and surface brightness distribution of the H$\alpha$ nebula, we propose the scenario that three major episodes of starburst/superwind activities which were initiated $\sim$10$^2$ Myr ago formed the extended ionized gas nebula of NGC 6240.
If the Universe is dominated by cold dark matter and dark energy as in the currently popular LCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M > ~10^14 Msun appearing at around 6 Gyrs after the Big Bang (z ~ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few x 10^13 Msun at redshifts between z=0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited samples of galaxies using a combination of spectroscopic and photometric redshifts. We analyze the Millennium simulation data in a similar way to the analysis of the observational data in order to test the LCDM cosmology. We find that there are too many massive structures (M > 7 x 10^13 Msun) observed at z > 2 in comparison with the simulation predictions by a factor of a few, giving a probability of < 1/2500 of the observed data being consistent with the simulation. Our result suggests that massive structures have emerged early, but the reason for the discrepancy with the simulation is unclear. It could be due to the limitation of the simulation such as the lack of key, unrecognized ingredients (strong non-Gaussianity or other baryonic physics), or simply a difficulty in the halo mass estimation from observation, or a fundamental problem of the LCDM cosmology. On the other hand, the over-abundance of massive structures at high redshifts does not favor heavy neutrino mass of ~ 0.3 eV or larger, as heavy neutrinos make the discrepancy between the observation and the simulation more pronounced by a factor of 3 or more.
Low-redshift active galactic nuclei (AGNs) with extremely blue optical
spectral indices are shown to have a mean, velocity-averaged, broad-line
H$\alpha$/H$\beta$ ratio of $\thickapprox 2.72 \pm 0.04$, consistent with the
Baker-Menzel Case B value. Comparison of a wide range of properties of the very
bluest AGNs with those of a luminosity-matched subset of the Dong et al. blue
AGN sample indicates that the only difference is the internal reddening.
Ultraviolet fluxes are brighter for the bluest AGNs by an amount consistent
with the flat AGN reddening curve of Gaskell et al. (2004). The lack of a
significant difference in the GALEX (FUV--NUV) colour index strongly rules out
a steep SMC-like reddening curve and also argues against an intrinsically
harder spectrum. For very blue AGNs the Ly$\alpha$/H$\beta$ ratio is also
consistent with being the Case B value. The Case B ratios provide strong
support for the self-shielded broad-line model of Gaskell, Klimek & Nazarova.
It is proposed that the greatly enhanced Ly$\alpha$/H$\beta$ ratio at very high
velocities is a consequence of continuum fluorescence in the Lyman lines (Case
C).
Reddenings of AGNs mean that the far-UV luminosity is underestimated by an
order of magnitude. This will be the main cause of the discrepancies between
measured accretion disc sizes and the predictions of simple accretion disc
theory. The greater luminosity of AGNs also resolves the photon underproduction
problem for the intergalactic medium. The total mass in lower mass supermassive
black holes must be greater than hitherto estimated.
We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for $K_s \ge 14$ Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebulae, and are likely to come from massive progenitor populations, and themselves be more massive than any sample of planetary nebulae known. Our survey has identified thousands of such candidates.
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