arXiv subjects

J. K. Kotilainen

Publications and source records attributed to J. K. Kotilainen.

At least 19 recordsLinked to original sources

arXiv2025

High resolution ALMA observations of H$_2$S in LIRGS (Dense gas and shocks in outflows and CNDs)

Molecular gas plays a critical role in regulating star formation and nuclear activity in galaxies. Sulphur bearing molecules, such as H2S, are sensitive to the physical and chemical environments in which they reside and are potential tracers of shocked, dense gas in galactic outflows and active galactic nuclei (AGN). We aim to investigate the origin of H2S emission and its relation to dense gas and outflow activity in the central regions of nearby infrared luminous galaxies. We present ALMA Band 5 observations of the ortho H2S 1(1,0) 1(0,1) transition in three nearby galaxies: NGC 1377, NGC 4418, and NGC 1266. We perform radiative transfer modelling using RADEX to constrain the physical conditions of the H2S emitting gas and compare the results to ancillary CO and continuum data. We detect compact H2S emission in all three galaxies, arising from regions smaller than approximately 150 parsecs. The H2S spectral profiles exhibit broad line wings, suggesting an association with outflowing or shocked gas. In NGC 4418, H2S also appears to be tracing gas that is counterrotating. A peculiar red shifted emission feature may correspond to inflowing gas, or possibly a slanted outflow. RADEX modelling indicates that the H2S emitting gas has high densities (molecular hydrogen density greater than 10^7 cm^-3) and moderately warm temperatures (between 40 and 200 Kelvin). The derived densities exceed those inferred from CO observations, implying that H2S traces denser regions of the interstellar medium.

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arXiv2022

Low-redshift quasars in the SDSS Stripe 82 -- III MOS observations

We present multi object optical spectroscopy of the galaxies in the environment of 12 low-redshift (z < 0.5) quasars and of 11 inactive massive galaxies chosen to match the properties of the quasar host galaxies to probe physical association and possible events of recent star formation. The quasars are selected from a sample of QSOs in the SDSS Stripe82 region for which both the host galaxy and the large scale environments were previously investigated. The new observations complement those reported in our previous works on close companion galaxies of nearby quasars. For the whole dataset we find that for about half (19 out of 44 ) of the observed QSOs there is at least one associated companion galaxy. In addition to the new spectroscopic observations, we add data from the SDSS database for the full sample of objects. We find that the incidence of companion galaxies in the fields of QSO (17%) is not significantly different from that of inactive galaxies (19%) similar to quasar hosts in redshift and mass. Nevertheless, the companions of quasars exhibit more frequently emission lines than those of inactive galaxies, suggesting a moderate link between the nuclear activity and recent star formation in their environments.

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arXiv2017

On the role of the environments and star formation for quasar activity

We investigate the host galaxy and environment properties of a sample of 400 low z (<0.5) quasars that were imaged in the SDSS Stripe82. We can detect and study the properties of the host galaxy for more than 75% of the data sample. We discover that quasar are mainly hosted in luminous galaxies of absolute magnitude M* -3 < M(R) < M* and that in the quasar environments the galaxy number density is comparable to that of inactive galaxies of similar luminosities. For these quasars we undertake also a study in u,g,r,i and z SDSS bands and again we discover that the mean colours of the quasar host galaxy it is not very different with respect to the values of the sample of inactive galaxies. For a subsample of low z sources the imaging study is complemented by spectroscopy of quasar hosts and of close companion galaxies. This study suggests that the supply and cause of the nuclear activity depends only weakly on the local environment of quasars. Contrary to past suggestions, for low redshift quasar there is a very modest connection between recent star formation and the nuclear activity.

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arXiv2017

Evidence of bar--driven secular evolution in the gamma--ray narrow--line Seyfert 1 galaxy FBQS J164442.5+261913

We present near--infrared (NIR) imaging of FBQS J164442.5+261913, one of the few $γ$--ray emitting Narrow Line Seyfert 1 ($γ-$NLSy1) galaxies detected at high significance level by $Fermi$--LAT. This study is the first morphological analysis performed of this source and the third performed of this class of objects. Conducting a detailed two--dimensional modeling of its surface brightness distribution and analysing its $J-K_s$ colour gradients, we find that FBQS J164442.5+261913 is statistically most likely hosted by a barred lenticular galaxy (SB0). We find evidence that the bulge in the host galaxy of FBQS J164442.5+261913 is not classical but pseudo, against the paradigm of powerful relativistic jets exclusively launched by giant ellipticals. Our analysis, also reveal the presence of a ring with diameter equalling the bar length ($r_{bar} = 8.13\ \textrm{kpc}\pm 0.25$), whose origin might be a combination of bar--driven gas rearrangement and minor mergers, as revealed by the apparent merger remnant in the $J$--band image. In general, our results suggest that the prominent bar in the host galaxy of FBQS J164442.5+261913 has mostly contributed to its overall morphology driving a strong secular evolution, which plays a crucial role in the onset of the nuclear activity and the growth of the massive bulge. Minor mergers, in conjunction, are likely to provide the necessary fresh supply of gas to the central regions of the host galaxy.

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arXiv2016

Low redshift quasars in the SDSS Stripe 82: Associated companion galaxies and signature of star formation

We obtained optical spectroscopy of close (< 80 kpc) companion objects of a sample of 12 low redshift quasars (z < 0.3 ) selected from the SDSS Stripe82 area and that are in the subsample of 52 QSOs for which both multicolor host galaxies properties and galaxy environment was recently investigated in detail. We found that for 8 out of 12 sources the companion galaxy is associated to the QSO having a difference of radial velocity that is less than 400 km/s. Many of these associated companions exhibit [OII] $λ$3727 Å~ emission lines suggestive of episodes of (recent) star formation possibly induced by past interactions. The SFR of the companion galaxies as derived from [OII] line luminosity is, however, modest, with a median value of 1.0 +-0.8 M_sun/yr, and the emission lines are barely consistent with expectation from gas ionization by the QSO. The role of the QSO for inducing star formation in close companion galaxies appears meager. For three objects we also detect the starlight spectrum of the QSO host galaxy which is characterized by absorption lines of old stellar population and [OII] emission line.

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arXiv2016

Discovery of a pseudobulge galaxy launching powerful relativistic jets

Supermassive black holes launching plasma jets at close to speed of light, producing gamma-rays, have ubiquitously been found to be hosted by massive elliptical galaxies. Since elliptical galaxies are generally believed to be built through galaxy mergers, active galactic nuclei (AGN) launching relativistic jets are associated to the latest stages of galaxy evolution. We have discovered a pseudo-bulge morphology in the host galaxy of the gamma-ray AGN PKS 2004-447. This is the first gamma-ray emitter radio loud AGN found to be launched from a system where both black hole and host galaxy have been actively growing via secular processes. This is evidence for an alternative black hole-galaxy co-evolutionary path to develop powerful relativistic jets that is not merger-driven.

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arXiv2016

The host galaxies of active galactic nuclei with powerful relativistic jets

We present deep Near-infrared (NIR) images of a sample of 19 intermediate-redshift ($0.3 10^{27}$ WHz$^{-1}$), previously classified as flat-spectrum radio quasars. We also compile host galaxy and nuclear magnitudes for blazars from literature. The combined sample (this work and compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities $L_{1.4GHz} \sim 10^{23.7} - 10^{28.3}$~WHz$^{-1}$, allowing us to divide our sample into high-luminosity blazars (HLBs) and low-luminosity blazars (LLBs). The host galaxies of our sample are bright and seem to follow the $μ_{e}$-$R_{eff}$ relation for ellipticals and bulges. The two populations of blazars show different behaviours in the \mnuc - \mbulge plane, where a statistically significant correlation is observed for HLBs. Although it may be affected by selection effects, this correlation suggests a close coupling between the accretion mode of the central supermassive black hole and its host galaxy, that could be interpreted in terms of AGN feedback. Our findings are consistent with semi--analytical models where low--luminosity AGN emit the bulk of their energy in the form of radio jets, producing a strong feedback mechanism, and high--luminosity AGN are affected by galaxy mergers and interactions, which provide a common supply of cold gas to feed both nuclear activity and star formation episodes.

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arXiv2015

Low redshift quasars in the SDSS Stripe 82. Host galaxy colors and close environment

We present a photometrical and morphological multicolor study of the properties of low redshift (z<0.3) quasar hosts based on a large and homogeneous dataset of quasars derived from the Sloan Digital Sky Survey (DR7). We used quasars that were imaged in the SDSS Stripe82 that is up to 2 mag deeper than standard Sloan images. This sample is part of a larger dataset of ~400 quasars at z<0.5 for which both the host galaxies and their galaxy environments were studied (Falomo et al. 2014,Karhunen et al. 2014). For 52 quasars we undertake a study of the color of the host galaxies and of their close environments in u,g,r,i and z bands. We are able to resolve almost all the quasars in the sample in the filters g,r,i and z and also in $u$ for about 50% of the targets. We found that the mean colors of the QSO host galaxy (g-i=0.82+-0.26; r-i=0.26+-0.16 and u-g=1.32+-0.25) are very similar to the values of a sample of inactive galaxies matched in terms of redshift and galaxy luminosity with the quasar sample. There is a suggestion that the most massive QSO hosts have bluer colors.Both quasar hosts and the comparison sample of inactive galaxies have candidates of close ($<$ 50 kpc) companion galaxies for ~30% of the sources with no significant difference between active and inactive galaxies. We do not find significant correlation between the central black hole (BH) mass and the quasar host luminosity that appears to be extra luminous at a given BH mass with respect to the local relation (M_BH -- M_host) for inactive galaxies. This confirms previous suggestion that a substantial disc component, not correlated to the BH mass, is present in the galaxies hosting low z quasars. These results support a scenario where the activation of the nucleus has negligible effects on the global structural and photometrical properties of the hosting galaxies.

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arXiv2015

The warm molecular gas and dust of Seyfert galaxies: two different phases of accretion?

The distribution of warm molecular gas (1000--3000 K), traced by the near-IR H$_2$ 2.12 $μ$m line, has been imaged with a resolution $<0.5$ arcsec in the central 1 kpc of seven nearby Seyfert galaxies. We find that this gas is highly concentrated towards the central 100 pc and that its morphology is often symmetrical. Lanes of warm H$_2$ gas are observed only in three cases (NGC\,1068, NGC\,1386 and Circinus) for which the morphology is much wider and extended than the dust filaments. We conclude that there is no one-to-one correlation between dust and warm gas. This indicates that, if the dust filaments and lanes of warm gas are radial streaming motions of fuelling material, they must represent \textit{two different phases of accretion}: the dust filaments represent a colder phase than the gas close to the nucleus (within $\sim$100 pc). We predict that the morphology of the nuclear dust at these scales should resemble that of the cold molecular gas (e.g. CO at 10--40 K), as we show for CenA and NGC\,1566 by Atacama Large Millimeter/submillimeter Array (ALMA) observations, whereas the inner H$_2$ gas traces a much warmer phase of material identified with warmer (40-500 K) molecular gas such as CO(6-5) or HCN (as shown by ALMA for NGC\,1068 and NGC\,1097). We also find that X-ray heating is the most likely dominant excitation mechanism of the H$_{2}$ gas for most sources.

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arXiv2014

Low redshift quasars in the SDSS Stripe 82. The local environments

We study the environments of low redshift (z < 0.5) quasars based on a large and homogeneous dataset from the Stripe 82 region of the Sloan Digital Sky Survey (SDSS). We have compared the < 1 Mpc scale envi- ronments of 302 quasars that were resolved in our recent study to those of 288 inactive galaxies with closely matched redshifts. Crucially, the lu- minosities of the inactive galaxies and the quasar host galaxies are also closely matched, unlike in most previous studies. The environmental overdensities were studied by measuring the num- ber density of galaxies within a projected distance of 200 kpc to 1 Mpc. The galaxy number density of the quasar environments is comparable to that of the inactive galaxies with similar luminosities, both classes of ob- jects showing significant excess compared to the background galaxy density for distances < 400 kpc. There is no significant dependence of the galaxy number density on redshift, quasar or host galaxy luminosity, black hole mass or radio loudness. This suggests that the fueling and triggering of the nuclear activity is only weakly dependent on the local environment of quasars, and the quasar phase may be a short-lived common phase in the life cycle of all massive galaxies.

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arXiv2014

The extent of the MgII absorbing circum-galactic medium of quasars

We investigate the extent and the properties of the MgII cool, low-density absorbing gas located in the halo and in the circum-galactic environment of quasars, using a sample of 31 projected quasar pairs with impact parameter pd<200kpc in the redshift range 0.5 0.3Ang. ranges from fc~1.0 at pd<65kpc to fc~0.2 at pd>150kpc, and appears to be higher than for galaxies. Our findings support a scenario where the luminosity/mass of the host galaxies affect the extent and the richness of the absorbing MgII circum-galactic medium.

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arXiv2014

Low redshift quasars in the SDSS Stripe 82. The host galaxies

We present a photometrical and morphological study of the properties of low redshift (z < 0.5) quasars based on a large and homogeneous dataset of objects derived from the Sloan Digital Sky Survey (DR7). This study over number by a factor about 5 any other previous study of QSO host galaxies at low redshift undertaken either on ground or on space surveys. We used about 400 quasars that were imaged in the SDSS Stripe82 that is up to 2 mag deeper than standard Sloan images. For these quasars we undertake a study of the host galaxies and of their environments. In this paper we report the results for the quasar hosts. We are able to detect the host galaxy for more than 3/4 of the whole dataset and characterise the properties of their hosts. We found that QSO hosts are dominated by luminous galaxies of absolute magnitude M*-3 < M(R) < M*. For the unresolved objects we computed a upper limit to the host luminosity. For each well resolved quasar we are also able to characterise the morphology of the host galaxy that turn out to be more complex than what found in previous studies. QSO are hosted in a variety of galaxies from pure ellipticals to complex/composite morphologies that combine spheroids, disk, lens and halo. The black hole mass of the quasar, estimated from the spectral properties of the nuclei, are poorly correlated with the total luminosity of the host galaxy. However, taking into account only the bulge component we found a significant correlation between the BH mass and the bulge luminosity of the host.

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arXiv2014

Super Star Clusters in Luminous Infrared Galaxies: the SUNBIRD Survey

We present recent results from an adaptive optics imaging survey of 40 Luminous IR Galaxies (LIRGs) searching for obscured core collapse supernovae and studying the galaxies themselves. Here, in particular, we discuss the Super Star Clusters (SSC) populations in the LIRGs. We have constructed the first statistically significant samples of Luminosity Functions (LF) of SSCs in the near-IR, and find evidence that the LF slopes in LIRGs are shallower than in more quiescent spiral galaxies. Distance and blending effects were investigated in detail paving the way for SSC studies further out than done previously. We have also correlated the luminosities of the brightest clusters with the star formation rates (SFR) of the hosts. The relation is similar, though somewhat steeper than that found in the optical and at lower SFR levels, suggesting systematic extinction and/or age effects. We find that the characteristics of the relation suggest an underlying physical driver rather than solely a size-of-sample effect. In particular, a truncated luminosity/mass function would naturally explain the small scatter we find. Finally, we are modelling the ages and masses of our near-IR detected clusters in conjunction with HST optical data and present early results of using SSC properties to trace the histories of the target LIRG systems.

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arXiv2012

On the cool gaseous haloes of quasars

We present optical spectroscopy of projected QSO pairs to investigate the MgII and the CIV absorption features imprinted on the spectrum of the background object by the gaseous halo surrounding the foreground QSO. We observed 13 projected pairs in the redshift range 0.7 1 Ang) are present also beyond a projected radius of ~70 kpc. If we take into account the mass of the galaxies as an additional parameter that influence the extent of the gaseous haloes, the distribution of the absorptions connected to the QSOs is consistent to that of galaxies. In the spectra of the foreground QSOs we do not detect any MgII absorption lines originated by the gas surrounding the QSO itself, but in 2 cases these features are present for CIV. The comparison between the absorption features observed in the transverse direction and those along the line of sight allows us to comment on the distribution of the absorbing gas and on the emission properties of the QSOs. Based on observations undertaken at the European Southern Observatory (ESO) Very Large Telescope (VLT) under Programmes 085.B-0210(A) and 086.B-0028(A).

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arXiv2012

Near-infrared spectroscopy of stellar populations in nearby spiral galaxies

We present high spatial resolution, medium spectral resolution near-infrared (NIR) H- and K-band long-slit spectroscopy for a sample of 29 nearby (z < 0.01) inactive spiral galaxies, to study the composition of their NIR stellar populations. These spectra contain a wealth of diagnostic stellar absorption lines, e.g. MgI 1.575 micron, SiI 1.588 micron, CO (6-3) 1.619 micron, MgI 1.711 micron, NaI 2.207 micron, CaI 2.263 micron and the 12CO and 13CO bandheads longward of 2.29 micron. We use NIR absorption features to study the stellar population and star formation properties of the spiral galaxies along the Hubble sequence, and we produce the first high spatial resolution NIR HK-band template spectra for low redshift spiral galaxies along the Hubble sequence. These templates will find applications in a variety of galaxy studies. The strength of the absorption lines depends on the luminosity and/or temperature of stars and, therefore, spectral indices can be used to trace the stellar population of galaxies. The entire sample testifies that the evolved red stars completely dominate the NIR spectra, and that the hot young star contribution is virtually nonexistent.

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arXiv2011

The host galaxy of the BL Lacertae object 1ES 0647+250 and its imaging redshift

Since no spectroscopic redshift is available for the remarkable BL Lac object 1ES 0647+250, we aim to derive an estimate of its distance from the properties of its host galaxy.We obtained a deep, high-resolution near-infrared H-band image of the BL Lacertae object 1ES 0647+250. We are able to detect the underlying host galaxy in the near-infrared. The host galaxy has an H-band magnitude of 16.9+-0.2 and an effective radius of 1.6+-0.3 arcsec. Using the imaging redshift method by Sbarufatti et al. (2005), we estimate a redshift z = 0.41+-0.06. This redshift is consistent with the previously reported imaging redshift estimate from the optical i'-band, z = 0.45+-0.08 by Meisner & Romani (2010), and with previously reported lower limits for the redshift. It is also in agreement with constraints from its gamma-ray emission. Imaging searches in the near-infrared, even with moderately sized telescopes, for the host galaxies of BL Lac objects at unknown redshift, are encouraged, as well as optical spectroscopy of 1ES 0647+250 with large telescopes to determine its spectroscopic redshift.

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arXiv2009

The quasar M_bh - M_host relation through Cosmic Time I - Dataset and black hole masses

We study the M_bh - M_host relation as a function of Cosmic Time in a sample of 96 quasars from z=3 to the present epoch. In this paper we describe the sample, the data sources and the new spectroscopic observations. We then illustrate how we derive M_bh from single-epoch spectra, pointing out the uncertainties in the procedure. In a companion paper, we address the dependence of the ratio between the black hole mass and the host galaxy luminosity and mass on Cosmic Time.

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arXiv2009

The quasar M_bh - M_host relation through Cosmic Time II - Evidence for evolution from z=3 to the present age

We study the dependence of the M_bh - M_host relation on the redshift up to z=3 for a sample of 96 quasars the host galaxy luminosities of which are known. Black hole masses were estimated assuming virial equilibrium in the broad line regions (Paper I), while the host galaxy masses were inferred from their luminosities. With this data we are able to pin down the redshift dependence of the M_bh - M_host relation along 85 per cent of the Universe age. We show that, in the sampled redshift range, the M_bh - L_host relation remains nearly unchanged. Once we take into account the aging of the stellar population, we find that the M_bh / M_host ratio (Gamma) increases by a factor ~7 from z=0 to z=3. We show that Gamma evolves with z regardless of the radio loudness and of the quasar luminosity. We propose that most massive black holes, living their quasar phase at high-redshift, become extremely rare objects in host galaxies of similar mass in the Local Universe.

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