Abstract
Feedback likely plays a crucial role in resolving discrepancies between observations and theoretical predictions of dwarf galaxy properties. Stellar feedback was once believed to be ...sufficient to explain these discrepancies, but it has thus far failed to fully reconcile theory and observations. The recent discovery of energetic galaxy-wide outflows in dwarf galaxies hosting active galactic nuclei (AGNs) suggests that AGN feedback may have a larger role in the evolution of dwarf galaxies than previously suspected. In order to assess the relative importance of stellar versus AGN feedback in these galaxies, we perform a detailed Keck/KCWI optical integral field spectroscopic study of a sample of low-redshift star-forming (SF) dwarf galaxies that show outflows in ionized gas in their Sloan Digital Sky Survey spectra. We characterize the outflows and compare them to observations of AGN-driven outflows in dwarfs. We find that SF dwarfs have outflow components that have comparable widths (
W
80
) to those of outflows in AGN dwarfs, but are much less blueshifted, indicating that SF dwarfs have significantly slower outflows than their AGN counterparts. Outflows in SF dwarfs are spatially resolved and significantly more extended than those in AGN dwarfs. The mass-loss, momentum, and energy rates of star-formation-driven outflows are much lower than those of AGN-driven outflows. Our results indicate that AGN feedback in the form of gas outflows may play an important role in dwarf galaxies and should be considered along with SF feedback in models of dwarf galaxy evolution.
Abstract While stellar processes are believed to be the main source of feedback in dwarf galaxies, the accumulating discoveries of active galactic nuclei (AGN) in dwarf galaxies over recent years ...arouse the interest to also consider AGN feedback in them. Fast, AGN-driven outflows, a major mechanism of AGN feedback, have indeed been discovered in dwarf galaxies and may be powerful enough to provide feedback to their dwarf hosts. In this paper, we search for outflows traced by the blueshifted ultraviolet absorption features in three dwarf galaxies with AGN from the sample examined in our previous ground-based study. We confirm outflows traced by blueshifted absorption features in two objects and tentatively detect an outflow in the third object. In one object where the outflow is clearly detected in multiple species, photoionization modeling suggests that this outflow is located ∼0.5 kpc from the AGN, implying a galactic-scale impact. This outflow is much faster and possesses a higher kinetic energy outflow rate than starburst-driven outflows in sources with similar star formation rates, and is likely energetic enough to provide negative feedback to its host galaxy as predicted by simulations. Much broader (∼4000 km s −1 ) absorption features are also discovered in this object, which may have the same origin as that of broad absorption lines in quasars. Additionally, strong He ii λ 1640 emission is detected in both objects where the transition falls in the wavelength coverage and is consistent with an AGN origin. In one of these two objects, a blueshifted He ii λ 1640 emission line is clearly detected, likely tracing a highly ionized AGN wind.
Abstract
Local low-metallicity dwarf galaxies are relics of the early universe and are thought to hold clues into the origins of supermassive black holes. While recent studies are uncovering a ...growing population of active galactic nuclei (AGNs) in dwarf galaxies, the vast majority reside in galaxies with solar or supersolar metallicities and stellar masses comparable to that of the LMC. Using Multi-Unit Spectroscopic Explorer (MUSE) and Very Large Telescope observations, we report the detection of Fe
x
λ
6374 coronal line emission and a broad H
α
line in the nucleus of SDSS J094401.87−003832.1, a nearby (
z
= 0.0049) metal-poor dwarf galaxy almost 500 times less massive than the LMC. Unlike the emission from the lower-ionization nebular lines, the Fe
x
λ
6374 emission is compact and centered on the brightest nuclear source, with a spatial extent of ≈100 pc, similar to that seen in well-known AGNs. The Fe
x
luminosity is ≈10
37
erg s
−1
, within the range seen in previously identified AGNs in the dwarf-galaxy population. The Fe
x
emission has persisted over the roughly 19 yr time period between the SDSS and MUSE observations, ruling out supernovae as the origin for the emission. The FWHM of the broad component of the H
α
line is 446 ± 17 km s
−1
and its luminosity is ≈1.5 × 10
38
erg s
−1
, corresponding to a black hole mass of ≈ 3150
M
⊙
, in line with its stellar mass if virial mass relations and black hole–galaxy scaling relations apply in this mass regime. These observations, together with previously reported multiwavelength observations, can most plausibly be explained by the presence of an accreting intermediate-mass black hole in a primordial galaxy analog.
Detecting active black holes in dwarf galaxies has proven to be a challenge due to their small size and weak electromagnetic signatures. Mid-infrared variability has emerged as a promising tool that ...can be used to detect active low-mass black holes in dwarf galaxies. We analyzed 10.4 years of photometry from the ALL\(WISE\)/NEO\(WISE\) multi-epoch catalogs, identifying 25 objects with AGN-like variability. Independent confirmation of AGN activity was found in 68% of these objects using optical and near-infrared diagnostics. Notably, we discovered a near-infrared coronal line S IX \(\lambda\) 1.252 \(\mu\)m in J1205, the galaxy with the lowest stellar mass (log M\(_{*}\) = 7.5 M\(_{\odot}\)) and low metallicity (12 + log(O/H) = 7.46) in our sample. Additionally, we found broad Pa\(\alpha\) potentially from the BLR in two targets, and their implied black hole masses are consistent with black hole-stellar mass relations. Comparing non-variable galaxies with similar stellar masses and \(WISE\) \(W1-W2\) colors, we found no clear trends between variability and large-scale galaxy properties. However, we found that AGN activity likely causes redder \(W1-W2\) colors in variable targets, while for the non-variable galaxies, the contribution stems from strong star formation activity. A high incidence of optical broad lines was also observed in variable targets. Our results suggest that mid-infrared variability is an effective method for detecting AGN activity in low-mass galaxies and can help uncover a larger sample of active low-mass (\(<\) 10\(^{6}\) M\(_{\odot}\)) black holes in the universe.
While stellar processes are believed to be the main source of feedback in dwarf galaxies, the accumulating discoveries of AGN in dwarf galaxies over recent years arouse the interest to also consider ...AGN feedback in them. Fast, AGN-driven outflows, a major mechanism of AGN feedback, have indeed been discovered in dwarf galaxies and may be powerful enough to provide feedback to their dwarf hosts. In this paper, we search for outflows traced by the blueshifted ultraviolet absorption features in three dwarf galaxies with AGN from the sample examined in our previous ground-based study. We confirm outflows traced by blueshifted absorption features in two objects and tentatively detect an outflow in the third object. In one object where the outflow is clearly detected in multiple species, photoionization modeling suggests that this outflow is located \(\sim\)0.5 kpc from the AGN, implying a galactic-scale impact. This outflow is much faster and possesses higher kinetic energy outflow rate than starburst-driven outflows in sources with similar star formation rates, and is likely energetic enough to provide negative feedback to its host galaxy as predicted by simulations. Much broader (\(\sim\)4000 km s\(^{-1}\)) absorption features are also discovered in this object which may have the same origin as that of broad absorption lines in quasars. Additionally, strong He II \(\lambda\)1640 emission is detected in both objects where the transition falls in the wavelength coverage, and is consistent with an AGN origin. In one of these two objects, blueshifted He II emission line is clearly detected, likely tracing a highly-ionized AGN wind.
Feedback likely plays a crucial role in resolving discrepancies between observed and theoretical predictions of dwarf galaxy properties. Stellar feedback was once believed to be sufficient to explain ...these discrepancies, but it has thus far failed to fully reconcile theory and observations. The recent discovery of energetic galaxy-wide outflows in dwarf galaxies hosting Active Galactic Nuclei (AGN) suggests that AGN feedback may have a larger role in the evolution of dwarf galaxies than previously suspected. In order to assess the relative importance of stellar versus AGN feedback in these galaxies, we perform a detailed Keck/KCWI optical integral field spectroscopic study of a sample of low-redshift star-forming (SF) dwarf galaxies that show outflows in ionized gas in their SDSS spectra. We characterize the outflows and compare them to observations of AGN-driven outflows in dwarfs. We find that SF dwarfs have outflow components that have comparable widths (W\(_{80}\)) to those of outflows in AGN dwarfs, but are much less blue-shifted, indicating that SF dwarfs have significantly slower outflows than their AGN counterparts. The outflows in SF dwarfs are spatially resolved and significantly more extended than those in AGN dwarfs. The mass loss rates, momentum and energy rates of SF-driven outflows are much lower than those of AGN-driven outflows. Our results indicate that AGN feedback in the form of gas outflows may play an important role in dwarf galaxies and should be considered along with SF feedback in models of dwarf galaxy evolution.
Local low metallicity dwarf galaxies are relics of the early universe and hold clues into the origins of supermassive black holes (SMBHs). In recent work, coronal lines have been used to unveil a ...population of candidate accreting black holes in dwarf galaxies with gas phase metallicities and stellar masses well below the host galaxies of any previously known AGNs. Using MUSE/VLT observations, we report the detection of Fe X \(\lambda\)6374 coronal line emission and a broad H\(\alpha\) line in the nucleus of SDSS J094401.87\(-\)003832.1, a nearby (\(z=0.0049\)) metal poor dwarf galaxy almost 500 times less massive than the LMC. The Fe X \(\lambda\)6374 emission is compact and centered on the brightest nuclear source, with a spatial extent of \(\approx\)100 pc. The Fe X luminosity is \(\approx 10^{37}\) erg s\(^{-1}\), within the range seen in previously identified AGNs in the dwarf galaxy population. This line has never been observed in gas ionized by hot stars. While it can be produced in supernova ejecta, the Fe X flux from SDSS J094401.87\(-\)003832.1 has persisted over the ~19 year time period between the SDSS and MUSE observations, ruling out supernovae as the origin for the emission. The black hole mass measured from the broad H\(\alpha\) FWHM and luminosity is \(\approx 3150\) M\(_\odot\), in line with its stellar mass if virial mass relations and black hole-galaxy scaling relations apply in this mass regime. These observations, together with previously reported multi-wavelength observations, can most plausibly be explained by the presence of an accreting intermediate mass black hole in a primordial galaxy analog. However, we cannot rule out the possibility that current stellar population models of metal poor stars significantly under-predict the stellar ionizing photon flux, and that metal poor stars can produce an extreme ionizing spectrum similar to that produced by AGNs.
Background: Scrub typhus caused by Orientia tsutsugamushi is a vector-borne zoonotic infection endemic in several parts of the globe. The infection generally presents with fever and nonspecific ...clinical features but may lead to severe complications with a high mortality rate if untreated. Early diagnosis and timely management are therefore important. Serological diagnosis such as Weil-Felix test, indirect immunofluorescence assay, immunoglobulin (Ig) M/IgG ELISA, and rapid antibody detection assays are either less sensitive or laborious. Molecular detection by polymerase chain reaction (PCR) targeting specific gene targets of O. tsutsugamushi is warranted. Materials and Methods: We developed a real-time PCR assay targeting 47-KDa htrA gene for the specific diagnosis of the pathogen. The assay was evaluated in a buffy coat from whole blood or serum samples collected from patients presenting with acute febrile illness. Randomly selected samples were also tested for IgM by commercial IgM ELISA assay. Results: The real-time PCR assay was able to detect <1 genome copy per the PCR input and specific to O. tsutsugamushi on heterologous pathogens testing. The samples were negative by real-time PCR and 13 samples were positive by IgM ELISA. This study found a relatively low prevalence of scrub typhus in the population. Conclusion: The assay developed in this study could be a useful diagnostic tool for the detection of O. tsutsugamushi in clinical samples. The study also indicated the need for a wide epidemiological survey that could help determine appropriate health measures including treatment and prevention.
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