We present the first -- of a series -- study of the evolution of galaxies in compact groups over the past 3 Gyr. This paper focuses on the evolution of the nuclear activity and how it has been affected by the dense environment of the groups. Our anal
ysis is based on the largest multiwavelength compact group sample to-date, containing complete ultraviolet-to-infrared (UV-to-IR) photometry for 1,770 isolated groups (7,417 galaxies). We classified the nuclear activity of the galaxies based on optical emission line and mid-infrared diagnostic methods, as well as using spectral energy distribution fitting. We observe a 15% increase on the number of the AGN-hosting late-type galaxies found in dynamically old groups, over the past 3 Gyr, accompanied by the corresponding decrease of their circumnuclear star formation. Comparing our compact group results with those of local isolated field and interacting pair galaxies, we find no differences in the AGN at the same redshift range. Based on both optical and mid-IR colour classifications, we report the absence of Seyfert 1 nuclei and we attribute this to the low accretion rates, caused by the depletion of gas. We propose that the observed increase of LINER and Seyfert 2 nuclei (at low-zs), in the early-type galaxies of the dynamically young groups, is due to the morphological transformation of lenticular into elliptical galaxies. Finally, we show that at any given stellar mass, galaxies found in dynamically old groups are more likely to host an AGN. Our findings suggest that the depletion of gas, due to past star formation and tidal stripping, is the major mechanism driving the evolution of the nuclear activity in compact groups of galaxies.
Very Long Baseline Interferometry (VLBI) at radio wavelengths can provide astrometry accurate to 10 micro-arcseconds or better (i.e. better than the target GAIA accuracy) without being limited by dust obscuration. This means that unlike GAIA, VLBI ca
n be applied to star-forming regions independently of their internal and line-of-sight extinction. Low-mass young stellar objects (particularly T Tauri stars) are often non-thermal compact radio emitters, ideal for astrometric VLBI radio continuum experiments. Existing observations for nearby regions (e.g. Taurus, Ophiuchus, or Orion) demonstrate that VLBI astrometry of such active T Tauri stars enables the reconstruction of both the regions 3D structure (through parallax measurements) and their internal kinematics (through proper motions, combined with radial velocities). The extraordinary sensitivity of the SKA telescope will enable similar tomographic mappings to be extended to regions located several kpc from Earth, in particular to nearby spiral arm segments. This will have important implications for Galactic science, galactic dynamics and spiral structure theories.
We present $^{12}$CO(2-1) line and 1300 $mu$m continuum observations made with the Submillimeter Array (SMA) of the young star DG Tau B. We find, in the continuum observations, emission arising from the circumstellar disk surrounding DG Tau B. The $^
{12}$CO(2-1) line observations, on the other hand, revealed emission associated with the disk and the asymmetric outflow related with this source. Velocity asymmetries about the flow axis are found over the entire length of the flow. The amplitude of the velocity differences is of the order of 1 -- 2 km s$^{-1}$ over distances of about 300 -- 400 AU. We interpret them as a result of outflow rotation. The sense of the outflow and disk rotation is the same. Infalling gas from a rotating molecular core cannot explain the observed velocity gradient within the flow. Magneto-centrifugal disk winds or photoevaporated disk winds can produce the observed rotational speeds if they are ejected from a keplerian disk at radii of several tens of AU. Nevertheless, these slow winds ejected from large radii are not very massive, and cannot account for the observed linear momentum and angular momentum rates of the molecular flow. Thus, the observed flow is probably entrained material from the parent cloud. DG Tau B is a good laboratory to model in detail the entrainment process and see if it can account for the observed angular momentum.
The determination of accurate distances to star-forming regions are discussed in the broader historical context of astronomical distance measurements. We summarize recent results for regions within 1 kpc and present perspectives for the near and more distance future.
[abridged] We present optical integral field spectroscopy for a flux-limited sample of 19 QSOs at z<0.2 and spatially resolve their ionized gas properties at a physical resolution of 2-5kpc. The extended narrow line regions (ENLRs), photoionized by t
he radiation of AGN, have sizes of up to several kpc and correlate more strongly with the QSO continuum luminosity than with the integrated [OIII] luminosity. We find a relation of the form log(r)~(0.46+-0.04)log(L_5100), reinforcing the picture of an approximately constant ionization parameter for the ionized clouds across the ENLR. Besides the ENLR, we also find gas ionized by young massive stars in more than 50 per cent of the galaxies on kpc scales. In more than half of the sample, the specific star formation rates based on the extinction-corrected Ha luminosity are consistent with those of inactive disc-dominated galaxies, even for some bulge-dominated QSO hosts. Enhanced SFRs of up to 70Msun/yr are rare and always associated with signatures of major mergers. Comparison with the SFR based on the 60+100micron FIR luminosity suggests that the FIR luminosity is systematically contaminated by AGN emission and Ha appears to be a more robust and sensitive tracer for the star formation rate. Evidence for efficient AGN feedback is scarce in our sample, but some of our QSO hosts lack signatures of ongoing star formation leading to a reduced specific SFR with respect to the main sequence of galaxies. Based on 12 QSOs where we can make measurements, we find that on average bulge-dominated QSO host galaxies tend to fall below the mass-metallicity relation compared to their disc-dominated counterparts. While not yet statistically significant for our small sample, this may provide a useful diagnostic for future large surveys if this metal dilution can be shown to be linked to recent or ongoing galaxy interactions.
We present archival high angular resolution ($sim$ 2$$) $^{12}$CO(3-2) line and continuum submillimeter observations of the young stellar object HL Tau made with the Submillimeter Array (SMA). The $^{12}$CO(3-2) line observations reveal the presence
of a compact and wide opening angle bipolar outflow with a northeast and southwest orientation (P.A. = 50$^circ$), and that is associated with the optical and infrared jet emanating from HL Tau with a similar orientation. On the other hand, the 850 $mu$m continuum emission observations exhibit a strong and compact source in the position of HL Tau that has a spatial size of $sim$ 200 $times$ 70 AU with a P.A. $=$ 145$^circ$, and a dust mass of around 0.1 M$_odot$. These physical parameters are in agreement with values obtained recently from millimeter observations. This submillimeter source is therefore related with the disk surrounding HL Tau.
It is widely accepted that the distribution function of the masses of young star clusters is universal and can be purely interpreted as a probability density distribution function with a constant upper mass limit. As a result of this picture the mass
es of the most-massive objects are exclusively determined by the size of the sample. Here we show, with very high confidence, that the masses of the most-massive young star clusters in M33 decrease with increasing galactocentric radius in contradiction to the expectations from a model of a randomly sampled constant cluster mass function with a constant upper mass limit. Pure stochastic star formation is thereby ruled out. We use this example to elucidate how naive analysis of data can lead to unphysical conclusions.
We report on the filaments that develop self-consistently in a new numerical simulation of cloud formation by colliding flows. As in previous studies, the forming cloud begins to undergo gravitational collapse because it rapidly acquires a mass much
larger than the average Jeans mass. Thus, the collapse soon becomes nearly pressureless, proceeding along its shortest dimension first. This naturally produces filaments in the cloud, and clumps within the filaments. The filaments are not in equilibrium at any time, but instead are long-lived flow features, through which the gas flows from the cloud to the clumps. The filaments are long-lived because they accrete from their environment while simultaneously accreting onto the clumps within them; they are essentially the locus where the flow changes from accreting in two dimensions to accreting in one dimension. Moreover, the clumps also exhibit a hierarchical nature: the gas in a filament flows onto a main, central clump, but other, smaller-scale clumps form along the infalling gas. Correspondingly, the velocity along the filament exhibits a hierarchy of jumps at the locations of the clumps. Two prominent filaments in the simulation have lengths ~15 pc, and masses ~600 Msun above density n ~ 10^3 cm-3 (~2x10^3 Msun at n > 50 cm-3). The density profile exhibits a central flattened core of size ~0.3 pc and an envelope that decays as r^-2.5, in reasonable agreement with observations. Accretion onto the filament reaches a maximum linear density rate of ~30 Msun Myr^-1 pc^-1.
The aim of this work is confirming the optical identification of PSR B1133+16, whose candidate optical counterpart was detected in Very Large Telescope (VLT) images obtained back in 2003. We used new deep optical images of the PSR B1133+16 field obta
ined with both the 10.4 m Gran Telescopio Canarias (GTC) and the VLT in the g and B bands, respectively, to confirm the detection of its candidate optical counterpart and its coincidence with the most recent pulsars radio coordinates. We did not detect any object at the position of the pulsar candidate counterpart (B~28), measured in our 2003 VLT images. However, we tentatively detected an object of comparable brightness in both the 2012 GTC and VLT images, whose position is offset by ~3.03 from that of the pulsars candidate counterpart in the 2003 VLT images and lies along the pulsars proper motion direction. Accounting for the time span of ~9 years between the 2012 quasi-contemporary GTC and VLT images and the 2003 VLT one, this offset is consistent with the yearly displacement of the pulsar due to its proper motion. Therefore, both the flux of the object detected in the 2012 GTC and VLT images and its position, consistent with the proper motion-corrected pulsar radio coordinates, suggest that we have detected the candidate pulsar counterpart that has moved away from its 2003 discovery position.
We present (sub)millimeter line and continuum observations in a mosaicing mode of the massive star forming region Cepheus A East made with the Submillimeter Array (SMA). Our mosaic covers a total area of about 3$$ $times$ 12$$ centered in the HW 2/3
region. For the first time, this observational study encloses a high angular resolution ($sim$ 3$$) together with a large scale mapping of Cepheus A East. We report compact and high velocity $^{12}$CO(2-1) emission associated with the multiple east-west bright H$_2$ condensations present in the region. Blueshifted and redshifted gas emission is found towards the east as well as west of HW 2/3. The observations suggest the presence of multiple large-scale east-west outflows that seems to be powered at smaller scales by radio sources associated with the young stars HW2, HW3c and HW3d. A kinematical study of part of the data suggests that the molecular outflow powered by HW2 is precesing with time as recently reported. Our data reveal five periodic ejections of material separated approximately every 10$^circ$ as projected in the plane of the sky. The most recent ejections appear to move toward the plane of the sky. An energetic explosive event as the one that occurred in Orion BN/KL or DR21 does not explain the kinematics, and the dynamical times of the multiple ejections found here. The continuum observations only revealed a strong millimeter source associated with the HW 2/3 region. High angular resolution observations allow us to resolve this extended dusty object in only two compact sources (with spatial sizes of approximately 300 AU) associated with HW2 and HW3c. Finally, the bright optical/X-Ray HH 168 -- GDD37 object might be produced by strong shocks related with the outflow from HW3c.
