Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA close look at the dwarf AGN of NGC 4395: optical and near-IR integral field spectroscopy
84
0
0.0
(
0
)
Added by
Rogemar Andre Riffel
Publication date
2019
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Intermediate mass black holes (10$^3$-10$^5$ M$_odot$) in the center of dwarf galaxies are believed to be analogous to growing Active Galactic Nuclei (AGN) in the early Universe. Their characterization can provide insight about the early galaxies. We present optical and near-infrared integral field spectroscopy of the inner $sim$50 pc of the dwarf galaxy NGC4395, known to harbor an AGN. NGC 4395 is an ideal candidate to investigate the nature of dwarf AGN, as it is nearby ($dapprox4.4$ Mpc) enough to allow a close look at its nucleus. The optical data were obtained with the Gemini GMOS-IFU covering the 4500 A to 7300 A spectral range at a spatial resolution of 10 pc. The J and K-band spectra were obtained with the Gemini NIFS at spatial resolutions of $sim$5 pc. The gas kinematics show a compact, rotation disk component with a projected velocity amplitude of 25 km s$^{-1}$. We estimate a mass of $7.7times10^5$ M$_odot$ inside a radius of 10 pc. From the H$alpha$ broad line component, we estimate the AGN bolometric luminosity as $L_{ bol}=(9.9pm1.4)times10^{40}$ erg s$^{-1}$ and a mass $M_{ BH}=(2.5^{+1.0}_{-0.8})times10^5$ M$_odot$ for the central black hole. The mean surface mass densities for the ionized and molecular gas are in the ranges (1-2) M$_{odot} $pc$^{-2}$ and (1-4)$times10^{-3}$ M${_odot}$ pc$^{-2}$ and the average ratio between ionized and hot molecular gas masses is $sim$500. The emission-line flux distributions reveal an elongated structure at 24 pc west of the nucleus, which is blueshifted relative to the systemic velocity of the galaxy by $approx$30 km s$^{-1}$. We speculate that this structure is originated by the accretion of a gas-rich small satellite or by a low metallicity cosmic cloud.
rate research
Read More
We present optical light curves from the Transiting Exoplanet Survey Satellite (TESS) for the archetypical dwarf active galactic nucleus (AGN) in the nearby galaxy NGC 4395 hosting a $sim 10^5,M_odot$ supermassive black hole (SMBH). Significant variability is detected on timescales from weeks to hours before reaching the background noise level. The $sim$month-long, 30 minute-cadence, high-precision TESS light curve can be well fit by a simple damped random walk (DRW) model, with the damping timescale $tau_{rm DRW}$ constrained to be $2.3_{-0.7}^{+1.8}$~days ($1sigma$). NGC 4395 lies almost exactly on the extrapolation of the $tau_{rm DRW}-M_{rm BH}$ relation measured for AGNs with BH masses that are more than three orders of magnitude larger. The optical variability periodogram can be well fit by a broken power law with the high-frequency slope ($-1.88pm0.15$) and the characteristic timescale ($tau_{rm br}equiv 1/(2pi f_{rm br})=1.4_{-0.5}^{+1.9},$days) consistent with the DRW model within 1$sigma$. This work demonstrates the power of TESS light curves in identifying low-mass accreting SMBHs with optical variability, and a potential global $tau_{rm DRW}-M_{rm BH}$ relation that can be used to estimate SMBH masses with optical variability measurements.
Feedback likely plays a vital role in the formation of dwarf galaxies. While stellar processes have long been considered the main source of feedback, recent studies have revealed tantalizing signs of AGN feedback in dwarf galaxies. In this paper, we report the results from an integral-field spectroscopic study of a sample of eight dwarf galaxies with known AGN and suspected outflows. Outflows are detected in seven of them. The outflows are fast, with 50-percentile (median) velocity of up to $sim$240 km s$^{-1}$ and 80-percentile line width reaching $sim$1200 km s$^{-1}$, in clear contrast with the more quiescent kinematics of the host gas and stellar components. The outflows are generally spatially extended on a scale of several hundred pc to a few kpc, although our data do not clearly resolve the outflows in three targets. The outflows appear to be primarily photoionized by the AGN rather than shocks or young, massive stars. The kinematics and energetics of these outflows suggest that they are primarily driven by the AGN, although the star formation activity in these objects may also contribute to the energy input. A small but non-negligible portion of the outflowing material likely escapes the main body of the host galaxy and contributes to the enrichment of the circumgalactic medium. Overall, the impact of these outflows on their host galaxies is similar to those taking place in the more luminous AGN in the low-redshift universe.
We present high resolution images of NGC 2071-IR in the $J$, $H$, and $K$ bands and in the emission at 2.12 $mu$m of the v=$1-0$ $S$(1) line of molecular hydrogen. We also present moderate resolution K-band spectra of two young stellar objects, IRS 1 and IRS 3, within NGC 2071-IR, that are candidates sources of one or more of the outflows observed in the region. Two of the eight originally identified infrared point sources in NGC 2071-IR are binaries, and we identifiy two new sources, one coincident with the radio source VLA-1 and highly reddened. The H2 $Q$(3)/$S$(1) line intensity ratios at IRS 1 and IRS 3 yield high and very high extinctions, respectively, to them, as is implied by their near-infrared colors and K-band continuum slopes. The spectra also reveal the presence of hot, dense circumstellar molecular gas in each, suggesting that both are strong candidates for having energetic molecular outflows. We agree with a previous suggestion that IRS 1 is the likely source of an E-W-oriented outflow and conclude that this outflow is probably largely out of the plane of the sky. We also conclude that if IRS 3 is the source of the large scale NE-SW outflow, as has been previously suggested, its jet/wind must precess in order to explain the angular width of that outflow. We discuss the natures of the point sources and their probable contributions, if any, to the complex morphology of the H2 line emission.
We investigate the 2D excitation structure of the ISM in a sample of LIRGs and Seyferts using near-IR IFS. This study extends to the near-IR the well-known optical and mid-IR emission line diagnostics used to classify activity in galaxies. Based on the spatially resolved spectroscopy of prototypes, we identify in the [FeII]1.64/Br$gamma$ - H_2 1-0S(1)/Br$gamma$ plane regions dominated by the different heating sources, i.e. AGNs, young MS massive stars, and evolved stars i.e. supernovae. The ISM in LIRGs occupy a wide region in the near-IR diagnostic plane from -0.6 to +1.5 and from -1.2 to +0.8 (in log units) for the [FeII]/Br$gamma$ and H_2/Br$gamma$ line ratios, respectively. The corresponding median(mode) ratios are +0.18(0.16) and +0.02(-0.04). Seyferts show on average larger values by factors ~2.5 and ~1.4 for the [FeII]/Br$gamma$ and H_2/Br$gamma$ ratios, respectively. New areas and relations in the near-IR diagnostic plane are defined for the compact, high surface brightness regions dominated by AGN, young ionizing stars, and SNe explosions, respectively. In addition, the diffuse regions affected by the AGN radiation field cover an area similar to that of Seyferts, but with high values in [FeII]/Br$gamma$ that are not as extreme. The extended, non-AGN diffuse regions cover a wide area in the diagnostic diagram that overlaps that of individual excitation mechanisms (i.e. AGN, young stars, and SNe), but with its mode value to that of the young SF clumps. This indicates that the excitation conditions of the diffuse ISM are likely due to a mixture of the different ionization sources. The integrated line ratios in LIRGs show higher excitation conditions i.e. towards AGNs, than those measured by the spatially resolved spectroscopy. If this behaviour is representative, it would have clear consequences when classifying high-z, SF galaxies based on their near-IR integrated spectra.
We present new, near-infrared ($1.1 - 2.4$ $mu m$) high-contrast imaging of the debris disk around HD 15115 with the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) coupled with the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS). SCExAO/CHARIS resolves the disk down to $rho sim 0.2$ ($rm{r_{proj}} sim 10$ $rm{au}$), a factor of $sim 3-5$ smaller than previous recent studies. We derive a disk position angle of $rm{PA}$ $sim 279.4^circ - 280.5^circ$ and an inclination of $rm{i}$ $sim 85.3^circ - 86.2^circ$. While recent SPHERE/IRDIS imagery of the system could suggest a significantly misaligned two ring disk geometry, CHARIS imagery does not reveal conclusive evidence for this hypothesis. Moreover, optimizing models of both one and two ring geometries using differential evolution, we find that a single ring having a Hong-like scattering phase function matches the data equally well within the CHARIS field of view ($rho lesssim 1$). The disks asymmetry, well-evidenced at larger separations, is also recovered; the west side of the disk appears on average around 0.4 magnitudes brighter across the CHARIS bandpass between $0.25$ and $1$. Comparing STIS/50CCD optical photometry ($2000-10500$ $r{A}$) with CHARIS NIR photometry, we find a red (STIS/50CCD$-$CHARIS broadband) color for both sides of the disk throughout the $0.4 - 1$ region of overlap, in contrast to the blue color reported at similar wavelengths for regions exterior to $sim 2$. Further, this color may suggest a smaller minimum grain size than previously estimated at larger separations. Finally, we provide constraints on planetary companions, and discuss possible mechanisms for the observed inner disk flux asymmetry and color.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
