arXiv subjects

T. Minezaki

Publications and source records attributed to T. Minezaki.

At least 19 recordsLinked to original sources

arXiv2022

Detection of highly correlated optical and X-ray variations in SS Cygni with Tomo-e Gozen and NICER

We report on simultaneous optical and X-ray observations of the dwarf nova SS Cyg with Tomo-e Gozen/1.05 m Kiso Schmidt and Neutron star Interior Composition ExploreR (it NICER) / International Space Station (ISS). A total of four observations were carried out in the quiescent state and highly correlated light variations between the two wavelengths were detected. We have extracted local brightness peaks in the light curves with a binning interval of 1 sec, called `shots', and have evaluated time lags between the optical and X-ray variations by using a cross-correlation function. Some shots exhibit significant optical lags to X-ray variations and most of them are positive ranging from $+$0.26 to 3.11 sec, which have never been detected. They may be ascribable to X-ray reprocessing in the accretion disk and/or the secondary star. This analysis is possible thanks to the high timing accuracy and the high throughput of NICER and the matching capability of Tomo-e Gozen. Also, it is confirmed that the correlation between the optical and X-ray variations changed in the middle of one of our observation windows and the X-ray spectrum softer than 2 keV varied in accordance with the correlation.

astro-ph.CO↗

arXiv2021

Physical Characterization of Serendipitously Uncovered Millimeter-wave Line-emitting Galaxies at z~2.5 behind the Local Luminous Infrared Galaxy VV114

We present a detailed investigation of millimeter-wave line emitters ALMA J010748.3-173028 (ALMA-J0107a) and ALMA J010747.0-173010 (ALMA-J0107b), which were serendipitously uncovered in the background of the nearby galaxy VV114 with spectral scan observations at $λ$ = 2 - 3 mm. Via Atacama Large Millimeter/submillimeter Array (ALMA) detection of CO(4-3), CO(3-2), and [CI](1-0) lines for both sources, their spectroscopic redshifts are unambiguously determined to be $z= 2.4666\pm0.0002$ and $z=2.3100\pm0.0002$, respectively. We obtain the apparent molecular gas masses $M_{\rm gas}$ of these two line emitters from [CI] line fluxes as $(11.2 \pm 3.1) \times 10^{10} M_\odot$ and $(4.2 \pm 1.2) \times 10^{10} M_\odot$, respectively. The observed CO(4-3) velocity field of ALMA-J0107a exhibits a clear velocity gradient across the CO disk, and we find that ALMA-J0107a is characterized by an inclined rotating disk with a significant turbulence, that is, a deprojected maximum rotation velocity to velocity dispersion ratio $v_{\rm max}/σ_{v}$ of $1.3 \pm 0.3$. We find that the dynamical mass of ALMA-J0107a within the CO-emitting disk computed from the derived kinetic parameters, $(1.1 \pm 0.2) \times 10^{10}\ M_\odot$, is an order of magnitude smaller than the molecular gas mass derived from dust continuum emission, $(3.2\pm1.6)\times10^{11}\ M_{\odot}$. We suggest this source is magnified by a gravitational lens with a magnification of $μ\gtrsim10$, which is consistent with the measured offset from the empirical correlation between CO-line luminosity and width.

astro-ph.GA↗

arXiv2018

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 < z < 6.9

We report discovery of 41 new high-z quasars and luminous galaxies, which were spectroscopically identified at 5.7 < z < 6.9. This is the fourth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, based on the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the photometric candidates by a Bayesian probabilistic algorithm, and then carried out follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous papers, we have now spectroscopically identified 137 extremely-red HSC sources over about 650 deg2, which include 64 high-z quasars, 24 high-z luminous galaxies, 6 [O III] emitters at z ~ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown dwarfs). The new quasars span the luminosity range from M1450 ~ -26 to -22 mag, and continue to populate a few magnitude lower luminosities than have been probed by previous wide-field surveys. In a companion paper, we derive the quasar luminosity function at z ~ 6 over an unprecedentedly wide range of M1450 ~ -28 to -21 mag, exploiting the SHELLQs and other survey outcomes.

astro-ph.GA↗

arXiv2014

Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469

A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emission-line lags for Hbeta 4861 and He II 4686 and a central black hole mass measurement of about 10 million solar masses, consistent with previous measurements. A very low level of variability during the monitoring campaign precluded meeting our original goal of recovering velocity-delay maps from the data, but with the new Hbeta measurement, NGC 7469 is no longer an outlier in the relationship between the size of the Hbeta-emitting broad-line region and the AGN luminosity. It was necessary to detrend the continuum and Hbeta and He II 4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results.

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arXiv2014

Reverberation Measurements of the Inner Radius of the Dust Torus in 17 Seyfert Galaxies

We present the results of a dust reverberation survey for 17 nearby Seyfert 1 galaxies, which provides the largest homogeneous data collection for the radius of the innermost dust torus. A delayed response of the K-band light curve after the V-band light curve was found for all targets, and 49 measurements of lag times between the flux variation of the dust emission in the K band and that of the optical continuum emission in the V band were obtained. The lag times strongly correlated with the optical luminosity in the luminosity range of M_V=-16 to -22 mag, and the regression analysis was performed to obtain the correlation log $Δt$ (days) = -2.11 -0.2 M_V assuming $Δt \propto L^{0.5}$, which was theoretically expected. We discuss the possible origins of the intrinsic scatter of the dust lag-luminosity correlation, which was estimated to be about 0.13 dex, and we find that the difference of internal extinction and delayed response of changes in lag times to the flux variations could have partly contributed to intrinsic scatter. However, we could not detect any systematic change of the correlation with the subclass of the Seyfert type or the Eddington ratio. Finally, we compare the dust reverberation radius with the near-infrared interferometric radius of the dust torus and the reverberation radius of broad Balmer emission lines. The interferometric radius in the K band was found to be systematically larger than the dust reverberation radius in the same band by about a factor of two, which could be interpreted by the difference between the flux-weighted radius and the response-weighted radius of the innermost dust torus. The reverberation radius of the broad Balmer emission lines was found to be systematically smaller than the dust reverberation radius by about a factor of 4-5, which strongly supports the unified scheme of the Seyfert type of active galactic nuclei. (Abridged)

astro-ph.GA↗

arXiv2014

A New Method for Measuring Extragalactic Distances

We have pioneered a new method for the measurement of extragalactic distances. This method uses the time-lag between variations in the short wavelength and long wavelength light from an active galactic nucleus (AGN), based on a quantitative physical model of dust reverberation that relates the time-lag to the absolute luminosity of the AGN. We use the large homogeneous data set from intensive monitoring observations in optical and near-infrared wavelength bands with the dedicated 2-m MAGNUM telescope to obtain the distances to 17 AGNs in the redshift range z=0.0024 to z=0.0353. These distance measurements are compared with distances measured using Cepheid variable stars, and are used to infer that H_0= 73 +- 3 (random) km/s/Mpc. The systematic error in H_0 is examined, and the uncertainty in the size distribution of dust grains is the largest source of the systematic error, which is much reduced for a sample of AGNs for which their parameter values in the model of dust reverberation are individually measured. This AGN time-lag method can be used beyond 30 Mpc, the farthest distance reached by extragalactic Cepheids, and can be extended to high-redshift quasi-stellar objects.

astro-ph.CO↗

arXiv2014

Underluminous Type II Plateau Supernovae: II. Pointing towards moderate mass precursors

We present new data for five under-luminous type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) is analyzed together with similar objects studied in the past. All of them show a flat light curve plateau lasting about 100 days, an under luminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P-Cygni lines. A velocity of the ejected material below 10^3 km/s is inferred from measurements at the end of the plateau. The 56Ni masses ejected in the explosion are very small (less than 10^-2 solar masses). We investigate the correlations among 56Ni mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy (2003), according to which events showing brighter plateau and larger expansion velocities are expected to produce more 56Ni. We propose that these faint objects represent the low luminosity tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modeling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core-collapse of intermediate mass stars, in the mass range 10-15 solar masses.

astro-ph.SR↗

arXiv2012

Reverberation Mapping Results for Five Seyfert 1 Galaxies

We present the results from a detailed analysis of photometric and spectrophotometric data on five Seyfert 1 galaxies observed as a part of a recent reverberation mapping program. The data were collected at several observatories over a 140-day span beginning in 2010 August and ending in 2011 January. We obtained high sampling-rate light curves for Mrk 335, Mrk 1501, 3C120, Mrk 6, and PG2130+099, from which we have measured the time lag between variations in the 5100 Angstrom continuum and the H-beta broad emission line. We then used these measurements to calculate the mass of the supermassive black hole at the center of each of these galaxies. Our new measurements substantially improve previous measurements of MBH and the size of the broad line-emitting region for four sources and add a measurement for one new object. Our new measurements are consistent with photoionization physics regulating the location of the broad line region in active galactic nuclei.

astro-ph.CO↗

arXiv2010

Reverberation Mapping Measurements of Black Hole Masses in Six Local Seyfert Galaxies

We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hbeta reverberation lag measurements for several relatively low-luminosity AGNs. We have reliably measured thetime delay between variations in the continuum and Hbeta emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) R-L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hbeta time delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.

astro-ph.CO↗

arXiv2010

Evidence for Supernova-Synthesised Dust from the Rising Afterglow of GRB 071025 at z~5

We present observations and analysis of the broadband afterglow of Swift GRB 071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this redshift our simultaneous multicolour observations begin at ~30 s after the GRB trigger in the host frame and during the initial rising phase of the afterglow. We associate the light curve peak at 580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Gamma_0 ~ 200. The red spectral energy distribution (even in regions not affected by the Lyman-alpha break) provides secure evidence of a large dust column. However, the inferred extinction curve shows a prominent flat component between 2000-3000 Angstroms in the rest-frame, inconsistent with any locally observed template but well-fit by models of dust formed by supernovae. Time-dependent fits to the extinction profile reveal no evidence of dust destruction and limit the decrease in the extinction column to Delta A_3000 < 0.54 mag after t = 50 s in the rest frame. Our observations provide evidence of a transition in dust properties at z~5, in agreement with studies of high-z quasars, and suggest that SN-formed dust continues to dominate the opacity of typical galaxies at this redshift.

astro-ph.HE↗

arXiv2010

Suzaku Monitoring of the Seyfert 1 Galaxy NGC5548: Warm Absorber Location and its Implication for Cosmic Feedback

(Abridged) We present a two month Suzaku X-ray monitoring of the Seyfert 1 galaxy NGC 5548. The campaign consists of 7 observations. We analyze the response in the opacity of the gas that forms the ionized absorber to ionizing flux variations. Despite variations by a factor of 4 in the impinging continuum, the soft X-ray spectra of the source show little spectral variations, suggesting no response from the ionized absorber. A detailed time modeling confirms the lack of opacity variations for an absorbing component with high ionization. Instead, the models tentatively suggest that the ionization parameter of a low ionization absorbing component might be changing with the ionizing flux, as expected for gas in photoionization equilibrium. Using the lack of variations, we set an upper limit of n_e <2.0E7 cm-3 for the electron density of the gas forming the high ionization, high velocity component. This implies a large distance from the continuum source (R > 0.033 pc). If the variations in the low ionization component are real, they imply n_e >9.8E4 cm-3 and R < 3 pc. We discuss our results in terms of two different scenarios: a large scale outflow originating in the inner parts of the accretion disk, or a thermally driven wind originating much farther out. Given the large distance of the wind, the implied mass outflow rate is also large (Mw > 0.08 Maccr). The associated total kinetic energy deployed by the wind in the host galaxy (>1.2E56 erg) can be enough to disrupt the interstellar medium, possibly regulating large scale star formation. The total mass and energy ejected by the wind is still lower than the one required for cosmic feedback, even when extrapolated to quasar luminosities. Such feedback would require that we are observing the wind before it is fully accelerated.

astro-ph.CO↗

arXiv2009

Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051

We discuss the origin of the optical variations in the Narrow line Seyfert 1 galaxy NGC 4051 and present the results of a cross-correlation study using X-ray and optical light curves spanning more than 12 years. The emission is highly variable in all wavebands, and the amplitude of the optical variations is found to be smaller than that of the X-rays, even after correcting for the contaminating host galaxy flux falling inside the photometric aperture. The optical power spectrum is best described by an unbroken power law model with slope $α=1.4^{+0.6}_{-0.2}$ and displays lower variability power than the 2-10 keV X-rays on all time-scales probed. We find the light curves to be significantly correlated at an optical delay of $1.2^{+1.0}_{-0.3}$ days behind the X-rays. This time-scale is consistent with the light travel time to the optical emitting region of the accretion disc, suggesting that the optical variations are driven by X-ray reprocessing. We show, however, that a model whereby the optical variations arise from reprocessing by a flat accretion disc cannot account for all the optical variability. There is also a second significant peak in the cross-correlation function, at an optical delay of $39^{+2.7}_{-8.4}$ days. The lag is consistent with the dust sublimation radius in this source, suggesting that there is a measurable amount of optical flux coming from the dust torus. We discuss the origin of the additional optical flux in terms of reprocessing of X-rays and reflection of optical light by the dust.

astro-ph.GA↗

arXiv2009

Stellar population and dust extinction in an ultraluminous infrared galaxy at z=1.135

We present the detailed optical to far-infrared observations of SST J1604+4304, an ULIRG at z = 1.135. Analyzing the stellar absorption lines, namely, the CaII H & K and Balmer H lines in the optical spectrum, we derive the upper limits of an age for the stellar population. Given this constraint, the minimum {chi}^2 method is used to fit the stellar population models to the observed SED from 0.44 to 5.8um. We find the following properties. The stellar population has an age 40 - 200 Myr with a metallicity 2.5 Z_{sun}. The starlight is reddened by E(B-V) = 0.8. The reddening is caused by the foreground dust screen, indicating that dust is depleted in the starburst site and the starburst site is surrounded by a dust shell. The infrared (8-1000um) luminosity is L_{ir} = 1.78 +/- 0.63 * 10^{12} L_{sun}. This is two times greater than that expected from the observed starlight, suggesting either that 1/2 of the starburst site is completely obscured at UV-optical wavelengths, or that 1/2 of L_{ir} comes from AGN emission. The inferred dust mass is 2.0 +/- 1.0 * 10^8 M_{sun}. This is sufficient to form a shell surrounding the galaxy with an optical depth E(B-V) = 0.8. From our best stellar population model - an instantaneous starburst with an age 40 Myr, we infer the rate of 19 supernovae(SNe) per year. Simply analytical models imply that 2.5 Z_{sun} in stars was reached when the gas mass reduced to 30% of the galaxy mass. The gas metallcity is 4.8 Z_{sun} at this point. The gas-to-dust mass ratio is then 120 +/- 73. The inferred dust production rate is 0.24 +/- 0.12 M_{sun} per SN. If 1/2 of L_{ir} comes from AGN emission, the rate is 0.48 +/- 0.24 M_{sun} per SN. We discuss the evolutionary link of SST J1604+4304 to other galaxy populations in terms of the stellar masses and the galactic winds.

astro-ph.CO↗

arXiv2009

Reverberation Mapping Results from MDM Observatory

We present results from a multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from around the world. We measure broad line region (BLR) radii and black hole masses for six objects. A velocity-resolved analysis of the H_beta response shows the presence of diverse kinematic signatures in the BLR.

astro-ph.CO↗

arXiv2009

Diverse Broad Line Region Kinematic Signatures From Reverberation Mapping

A detailed analysis of the data from a high sampling rate, multi-month reverberation mapping campaign, undertaken primarily at MDM Observatory with supporting observations from telescopes around the world, reveals that the Hbeta emission region within the broad line regions (BLRs) of several nearby AGNs exhibit a variety of kinematic behaviors. While the primary goal of this campaign was to obtain either new or improved Hbeta reverberation lag measurements for several relatively low luminosity AGNs (presented in a separate work), we were also able to unambiguously reconstruct velocity-resolved reverberation signals from a subset of our targets. Through high cadence spectroscopic monitoring of the optical continuum and broad Hbeta emission line variations observed in the nuclear regions of NGC 3227, NGC 3516, and NGC 5548, we clearly see evidence for outflowing, infalling, and virialized BLR gas motions, respectively.

astro-ph.CO↗

arXiv2009

A Revised Broad-Line Region Radius and Black Hole Mass for the Narrow-Line Seyfert 1 NGC 4051

We present the first results from a high sampling rate, multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from telescopes around the world. The primary goal of this campaign was to obtain either new or improved Hbeta reverberation lag measurements for several relatively low luminosity AGNs. We feature results for NGC 4051 here because, until now, this object has been a significant outlier from AGN scaling relationships, e.g., it was previously a ~2-3sigma outlier on the relationship between the broad-line region (BLR) radius and the optical continuum luminosity - the R_BLR-L relationship. Our new measurements of the lag time between variations in the continuum and Hbeta emission line made from spectroscopic monitoring of NGC 4051 lead to a measured BLR radius of R_BLR = 1.87 (+0.54 -0.50) light days and black hole mass of M_BH = 1.73 (+0.55 -0.52) x 10^6 M_sun. This radius is consistent with that expected from the R_BLR-L relationship, based on the present luminosity of NGC 4051 and the most current calibration of the relation by Bentz et al. (2009a). We also present a preliminary look at velocity-resolved Hbeta light curves and time delay measurements, although we are unable to reconstruct an unambiguous velocity-resolved reverberation signal.

astro-ph.CO↗

arXiv2009

Type Ib Supernova 2008D associated with the Luminous X-ray Transient 080109: An Energetic Explosion of a Massive Helium Star

We present a theoretical model for supernova (SN) 2008D associated with the luminous X-ray transient 080109. The bolometric light curve and optical spectra of the SN are modelled based on the progenitor models and the explosion models obtained from hydrodynamic/nucleosynthetic calculations. We find that SN 2008D is a more energetic explosion than normal core-collapse supernovae, with an ejecta mass of Mej = 5.3 +- 1.0 Msun and a kinetic energy of E = 6.0 +- 2.5 x 10^{51} erg. The progenitor star of the SN has a 6-8 Msun He core with essentially no H envelope (< 5 x 10^{-4} Msun) prior to the explosion. The main-sequence mass of the progenitor is estimated to be Mms =20-25 Msun, with additional systematic uncertainties due to convection, mass loss, rotation, and binary effects. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. The mass of the central remnant is estimated as 1.6 - 1.8 Msun, which is near the boundary between neutron star and black hole formation.

astro-ph↗

arXiv2008

Long term optical and X-ray variability of the Seyfert galaxy Markarian 79

We present the results of concurrent X-ray and optical monitoring of the Seyfert 1 galaxy Mrk 79 over a period of more than five years. We find that on short to medium time-scales (days to a few tens of days) the 2-10 keV X-ray and optical u and V band fluxes are significantly correlated, with a delay between the bands consistent with zero days. We show that most of these variations may be well reproduced by a model where the short-term optical variations originate from reprocessing of X-rays by an optically thick accretion disc. The optical light curves, however, also display long time-scale variations over thousands of days, which are not present in the X-ray light curve. These optical variations must originate from an independent variability mechanism and we show that they can be produced by variations in the (geometrically) thin disc accretion rate as well as by varying reprocessed fractions through changes in the location of the X-ray corona.

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