arXiv subjects

B. Rothberg

Publications and source records attributed to B. Rothberg.

17 recordsLinked to original sources

arXiv2025

A High Resolution Search for Dual AGN Candidates in Mergers: A Pre-Selection Strategy using Keck AO

Accreting supermassive black holes (SMBHs) in galaxy mergers with separations $<$ 1 kpc are crucial to our understanding of SMBH growth, galaxy evolution, and SMBH binary evolution. Despite their importance, few are known, and most have been discovered serendipitously. In this work, we develop and test a method to systematically pre-select candidate advanced mergers likely to contain unresolved sub-kpc nuclear substructure constituting high-priority dual-AGN candidates for follow-up spectroscopy. By exploiting the survey area and astrometric precision of the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS), we identified 46 nearby advanced mergers that have red WISE colors ($W_1-W_2>0.5$) indicative of accretion activity and significant sub-arcsecond offsets between their optical and infrared coordinates as measured by SDSS and WISE. We conducted high-resolution adaptive optics (AO) observations with the Keck NIRC2 camera in the $K_p$ band ($2.124 \mu m$, $\Delta\lambda = 0.351 \mu m$) to search for unresolved substructure suggested by the optical-to-infrared offsets. We find that 20/46 (43\%) of the sample shows substructure tracing the SDSS/WISE offset and unresolved by SDSS , representing a higher yield than previous pre-selection techniques such as double-peaked [O III] or hard X-ray selection. These results demonstrate that the SDSS/WISE offset method provides an efficient pathway for identifying late-stage mergers and dual-AGN candidates for spectroscopic confirmation. Archival optical Hubble Space Telescope (HST) imaging reveals that substructure identified with Keck is often missed in the optical or erroneously identified due to partial obscuration, underscoring the importance of infrared studies of late-stage mergers.

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arXiv2023

Near-Infrared Observations of Outflows and YSOs in the Massive Star-Forming Region AFGL 5180

Methods: Broad- and narrow-band imaging of AFGL 5180 was made in the NIR with the LBT, in both seeing-limited ($\sim0.5\arcsec$) and high angular resolution ($\sim0.09\arcsec$) Adaptive Optics (AO) modes, as well as with HST. Archival ALMA continuum data was also utilized. Results: At least 40 jet knots were identified via NIR emission from H$_2$ and [FeII] tracing shocked gas. Bright jet knots outflowing from the central most massive protostar, S4, are detected towards the east of the source and are resolved in fine detail with the AO imaging. Additional knots are distributed throughout the field, likely indicating the presence of multiple driving sources. Sub-millimeter sources detected by ALMA are shown to be grouped in two main complexes, AFGL 5180 M and a small cluster $\sim15\arcsec$ to the south, AFGL 5180 S. From our NIR continuum images we identify YSO candidates down to masses of $\sim 0.1\:M_\odot$. Combined with the sub-mm sources, this yields a surface number density of such YSOs of $N_* \sim 10^3 {\rm pc}^{-2}$ within a projected radius of about 0.1 pc. Such a value is similar to those predicted by models of both Core Accretion from a turbulent clump environment and Competitive Accretion. The radial profile of $N_*$ is relatively flat on scales out to 0.2~pc, with only modest enhancement around the massive protostar inside 0.05~pc. Conclusions: This study demonstrates the utility of high-resolution NIR imaging, in particular with AO, for detecting outflow activity and YSOs in distant regions. The presented images reveal the complex morphology of outflow-shocked gas within the large-scale bipolar flow of a massive protostar, as well as clear evidence for several other outflow driving sources in the region. Finally, this work presents a novel approach to compare the observed YSO surface number density from our study against different models of massive star formation.

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arXiv2023

The SOUL view of IRAS20126+4104. Kinematics and variability of the H$_2$ jet from a massive protostar

We exploit the increased sensitivity of the recently installed AO SOUL at the LBT to obtain new high-spatial-resolution NIR images of the massive young stellar object IRAS20126+4104 and its outflow. We aim to derive the jet proper motions and kinematics, as well as to study its photometric variability by combining the novel performances of SOUL together with previous NIR images. We used both broad-band ($K_{s}$, $K'$) and narrow-band (Br$\gamma$, H2) observations from a number of NIR cameras (UKIRT/UFTI,SUBARU/CIAO,TNG/NICS,LBT/PISCES,and LBT/LUCI1) to derive maps of the continuum and the H$_2$ emission in the 2.12 $\mu$m line. Three sets of images, obtained with AO systems (CIAO,2003; FLAO,2012; SOUL,2020), allowed us to derive the proper motions of a large number of H$_2$ knots along the jet. Photometry from all images was used to study the jet variability. We derived knot proper motions in the range of 1.7-20.3 mas yr$^{-1}$ (i.e. 13-158 km s$^{-1}$ at 1.64 kpc, avg. outflow tangential velocity $\sim$ 80 km s$^{-1}$). The derived knot dynamical age spans a $\sim$ 200-4000 yr interval. A ring-like H$_2$ feature near the protostar location exhibits peculiar kinematics and may represent the outcome of a wide-angle wind impinging on the outflow cavity. Both H$_2$ geometry and velocities agree with those inferred from proper motions of the H$_2$O masers, located at a smaller distance from the protostar. Although the total H$_2$ line emission from the knots does not exhibit time variations at a $\widetilde{>}$ 0.3 mag level, we have found a clear continuum flux variation (radiation scattered by the dust in the cavity opened by the jet) which is anti-correlated between the blue-shifted and red-shifted lobes and may be periodic (with a period of $\sim$ 12-18 yr). We suggest that the continuum variability might be related to inner-disc oscillations which have also caused the jet precession.

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arXiv2022

A short gamma-ray burst from a proto-magnetar remnant

The contemporaneous detection of gravitational waves and gamma rays from the GW170817/GRB 170817A, followed by kilonova emission a day after, confirmed compact binary neutron-star mergers as progenitors of short-duration gamma-ray bursts (GRBs), and cosmic sources of heavy r-process nuclei. However, the nature (and lifespan) of the merger remnant and the energy reservoir powering these bright gamma-ray flashes remains debated, while the first minutes after the merger are unexplored at optical wavelengths. Here, we report the earliest discovery of bright thermal optical emission associated with the short GRB 180618A with extended gamma-ray emission, with ultraviolet and optical multicolour observations starting as soon as 1.4 minutes post-burst. The spectrum is consistent with a fast-fading afterglow and emerging thermal optical emission at 15 minutes post-burst, which fades abruptly and chromatically (flux density $F_{\nu} \propto t^{-\alpha}$, $\alpha=4.6 \pm 0.3$) just 35 minutes after the GRB. Our observations from gamma rays to optical wavelengths are consistent with a hot nebula expanding at relativistic speeds, powered by the plasma winds from a newborn, rapidly-spinning and highly magnetized neutron star (i.e. a millisecond magnetar), whose rotational energy is released at a rate $L_{\rm th} \propto t^{-(2.22\pm 0.14)}$ to reheat the unbound merger-remnant material. These results suggest such neutron stars can survive the collapse to a black hole on timescales much larger than a few hundred milliseconds after the merger, and power the GRB itself through accretion. Bright thermal optical counterparts to binary merger gravitational wave sources may be common in future wide-field fast-cadence sky surveys.

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arXiv2022

Orbital and dynamical analysis of the system around HR 8799. New astrometric epochs from VLT/SPHERE and LBT/LUCI

HR\,8799 is a young planetary system composed of 4 planets and a double debris belt. Being the first multi-planetary system discovered with the direct imaging technique, it has been observed extensively since 1998. This wide baseline of astrometric measurements, counting over 50 observations in 20 years, permits a detailed orbital and dynamical analysis of the system. To explore the orbital parameters of the planets, their dynamical history, and the planet-to-disk interaction, we made follow-up observations of the system during the VLT/SPHERE GTO program. We obtained 21 observations, most of them in favorable conditions. In addition, we observed HR\,8799 with the instrument LBT/LUCI. All the observations were reduced with state-of-the-art algorithms implemented to apply the spectral and angular differential imaging method. We re-reduced the SPHERE data obtained during the commissioning of the instrument and in 3 open-time programs to have homogeneous astrometry. The precise position of the 4 planets with respect to the host star was calculated by exploiting the fake negative companions method. To improve the orbital fitting, we also took into account all of the astrometric data available in the literature. From the photometric measurements obtained in different wavelengths, we estimated the planets' masses following the evolutionary models. We obtained updated parameters for the orbits with the assumption of coplanarity, relatively small eccentricities, and periods very close to the 2:1 resonance. We also refined the dynamical mass of each planet and the parallax of the system (24.49 $\pm$ 0.07 mas). We also conducted detailed $N$-body simulations indicating possible positions of a~putative fifth innermost planet with a mass below the present detection limits of $\simeq 3$~\MJup.

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arXiv2021

The peculiar short-duration GRB 200826A and its supernova

Gamma-ray bursts (GRBs) are classified as long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the merger of compact objects. GRB 200826A was a peculiar event, because by definition it was a SGRB, with a rest-frame duration of ~ 0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (z = 0.7486) motivated a comprehensive, multi-wavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution is in agreement with several LGRB-SNe. Analysis of the prompt GRB shows that this event follows the $E_{\rm p,i}-E_{\rm iso}$ relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical for LGRBs, but with one of the highest star-formation rates (SFR), especially with respect to its mass ($\log M_\ast/M_\odot = 8.6$, SFR $\sim 4.0 \,M_\odot$/yr). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB.

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arXiv2017

Testing for Shock-Heated X-ray Gas Around Compact Steep Spectrum Radio Galaxies

We present Chandra and XMM-Newton X-ray, VLA radio, and optical observations of three candidate Compact Steep Spectrum (CSS) radio galaxies. CSS sources are galactic scale and are presumably driving a shock through the ISM of their host galaxy. B3 1445+410 is a low excitation emission line CSS radio galaxy with possibly a hybrid Fanaroff-Riley FRI/II (or Fat Double) radio morphology. The Chandra observations reveal a point-like source which is well fit with a power law consistent with emission from a Doppler boosted core. 3C 268.3 is a CSS broad line radio galaxy whose Chandra data are consistent spatially with a point source centered on the nucleus and spectrally with a double power-law model. PKS B1017-325 is a low excitation emission line radio galaxy with a bent double radio morphology. While from our new spectroscopic redshift, PKS B1017-325 falls outside the formal definition of a CSS, the XMNM-Newton observations are consistent with ISM emission with either a contribution from hot shocked gas or non-thermal jet emission. We compile selected radio and X-ray properties of the nine bona fide CSS radio galaxies with X-ray detections so far. We find that 2/9 show X-ray spectroscopic evidence for hot shocked gas. We note that the counts in the sources are low and the properties of the 2 sources with evidence for hot shocked gas are typical of the other CSS radio galaxies. We suggest that hot shocked gas may be typical of CSS radio galaxies due to their propagation through their host galaxies.

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arXiv2016

Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality

We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12000 to 23000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by ~0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] = -2.4 to Solar. There are, however, significant differences between galaxies in the relative numbers of \emph{metal-rich} clusters, suggesting that they underwent significantly different histories of mergers with massive, gas-rich halos. Lastly, the proportion of metal-poor GCs rises especially rapidly outside projected radii R > 4 R_eff, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.

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arXiv2016

Obscured AGNs in Bulgeless Hosts discovered by WISE: The Case Study of SDSS J1224+5555

There is mounting evidence that supermassive black holes form and grow in bulgeless galaxies. However, a robust determination of the fraction of AGNs in bulgeless galaxies, an important constraint to models of supermassive black hole seed formation and merger-free models of AGN fueling, is unknown, since optical studies have been shown to be incomplete for low mass AGNs. In a recent study using the Wide-field Infrared Survey Explorer, we discovered hundreds of bulgeless galaxies that display mid-infrared signatures of extremely hot dust suggestive of powerful accreting massive black holes, despite having no signatures of black hole activity at optical wavelengths. Here we report X-ray follow-up observations of J122434.66+555522.3, a nearby (z=0.052) isolated bulgeless galaxy that contains an unresolved X-ray source detected at the 3 sigma level by XMM-Newton with an observed luminosity uncorrected for intrinsic absorption of L{2-10~keV}=1.1+/-0.4 10^40 ergs/s. Ground-based near-infrared spectroscopy with the Large Binocular Telescope together with multiwavelength observations from ultraviolet to millimeter wavelengths together suggest that J1224+5555 harbors a highly absorbed AGN with an intrinsic absorption of ~NH >10^24 cm^-2. The hard X-ray luminosity of the putative AGN corrected for absorption is L{2-10~keV}~3x10^42 ergs/s, which, depending on the bolometric correction factor, corresponds to a bolometric luminosity of the AGN of 6x10^43ergs/s - 3x10^44 erg/s, and a lower mass limit for the black hole of MBH~2x10^6 Msun, based on the Eddington limit.

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arXiv2016

First results from Faint Infrared Grism Survey (FIGS): first simultaneous detection of Lyman-alpha emission and Lyman break from a galaxy at z=7.51

Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyman-alpha emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on Hubble Space Telescope (HST), show a significant emission line detection (6 sigma) in multiple observational position angles (PA), with total integrated Ly{\alpha} line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is nearly a factor of four higher than the previous MOSFIRE spectroscopic observations of faint Ly{\alpha} emission at {\lambda} = 1.0347{\mu}m, yielding z = 7.5078+/- 0.0004. This is consistent with other recent observations implying that ground-based near-infrared spectroscopy underestimates total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyman-{\alpha} measurements. A 4-{\sigma} detection of the NV line in one PA also suggests a weak Active Galactic Nucleus (AGN), potentially making this source the highest-redshift AGN yet found. Thus, this observation from the Hubble Space Telescope clearly demonstrates the sensitivity of the FIGS survey, and the capability of grism spectroscopy to study the epoch of reionization.

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arXiv2012

A decrease of the gas exchanges between galaxies and the IGM, from 12 to 6 billion years ago

Using a representative sample of 65 intermediate mass galaxies at z \sim 0.6, we have inves- tigated the interplay between the main ingredients of chemical evolution: metal abundance, gas mass, stellar mass and SFR. All quantities have been estimated using deep spectroscopy and photometry from UV to IR and assuming an inversion of the Schmitt-Kennicutt law for the gas fraction. Six billion years ago, galaxies had a mean gas fraction of 32% \pm 3, i.e. twice that of their local counterparts. Using higher redshift samples from the literature, we explore the gas-phases and estimate the evolution of the mean gas fraction of distant galaxies over the last 11 Gy. The gas fraction increases linearly at the rate of 4% per Gyr from z \sim 0 to z \sim 2.2. We also demonstrate for a statistically representative sample that < 4% of the z \sim 0.6 galaxies are undergoing outflow events, in sharp contrast with z \sim 2.2 galaxies. The observed co-evolution of metals and gas over the past 6 Gyr favours a scenario in which the population of intermediate mass galaxies evolved as closed-systems, converting their own gas reservoirs into stars.

astro-ph.CO↗

arXiv2011

A Link to the Past: Using Markov Chain Monte Carlo Fitting to Constrain Fundamental Parameters of High-Redshift Galaxies

We have a developed a new method for fitting spectral energy distributions (SEDs) to identify and constrain the physical properties of high-redshift (4 < z < 8) galaxies. Our approach uses an implementation of Bayesian based Markov Chain Monte Carlo (PiMC^2) that allows us to compare observations to arbitrarily complex models and to compute 95% credible intervals that provide robust constraints for the model parameters. The work is presented in 2 sections. In the first, we test PiMC^2 using simulated SEDs to not only confirm the recovery of the known inputs but to assess the limitations of the method and identify potential hazards of SED fitting when applied specifically to high redshift (z>4) galaxies. Our tests reveal five critical results: 1) the ability to confidently constrain metallicity, population ages, and Av all require photometric accuracy better than what is currently achievable (i.e. less than a few percent); 2) the ability to confidently constrain stellar masses (within a factor of two) can be achieved without the need for high-precision photometry; 3) the addition of IRAC photometry does not guarantee that tighter constraints of the stellar masses and ages can be defined; 4) different assumptions about the star formation history can lead to significant biases in mass and age estimates; and 5) we are able to constrain stellar age and Av of objects that are both young and relatively dust free. In the second part of the paper we apply PiMC^2 to 17 4 6 galaxies. Using PiMC^2, we are able to constrain the stellar mass of these objects and in some cases their stellar age and find no evidence that any of these sources formed at a redshift much larger than z_f=8, a time when the Universe was ~ 0.6 Gyr old.

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arXiv2010

Extreme Starbursts in the Local Universe

The "Extreme starbursts in the local universe" workshop was held at the Insituto de Astrofisica de Andalucia in Granada, Spain on 21-25 June 2010. Bearing in mind the advent of a new generation of facilities such as JWST, Herschel, ALMA, eVLA and eMerlin, the aim of the workshop was to bring together observers and theorists to review the latest results. The purpose of the workshop was to address the following issues: what are the main modes of triggering extreme starbursts in the local Universe? How efficiently are stars formed in extreme starbursts? What are the star formation histories of local starburst galaxies? How well do the theoretical simulations model the observations? What can we learn about starbursts in the distant Universe through studies of their local counterparts? How important is the role of extreme starbursts in the hierarchical assembly of galaxies? How are extreme starbursts related to the triggering of AGN in the nuclei of galaxies? Overall, 41 talks and 4 posters with their corresponding 10 minutes short talks were presented during the workshop. In addition, the workshop was designed with emphasis on discussions, and therefore, there were 6 discussion sessions of up to one hour during the workshop. Here is presented a summary of the purposes of the workshop as well as a compilation of the abstracts corresponding to each of the presentations. The summary and conclusions of the workshop along with a description of the future prospects by Sylvain Veilleux can be found in the last section of this document. A photo of the assistants is included.

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arXiv2009

The Impact of Stellar Populations on the Dynamics of Merger Remnants

Many studies and simulations suggest gas-rich mergers do not contribute significantly to the overall star-formation rate and total mass function of galaxies. The velocity dispersions (sigma) of Luminous & Ultraluminous Infrared Galaxies measured using the 1.62 or 2.29 micron CO bandheads imply they will form m < m* ellipticals. Yet, sigma's obtained with the Calcium II triplet (CaT) at 0.85 micron suggest all types of mergers will form m > m* ellipticals. Presented here are recent results, based on high-resolution imaging and multi-wavelength spectroscopy, which demonstrate the dominance of a nuclear disk of Red Supergiants (RSG) or Asymptotic Giant Branch (AGB) stars in the near-infrared bands, where dust obscuration does not sufficiently block their signatures. The presence of these stars severely biases the dynamical mass. At I-band, where dust can sufficiently block RSG or AGB stars, LIRGs populate the Fundamental Plane over a large dynamic range and are virtually indistinguishable from elliptical galaxies.

astro-ph.CO↗

arXiv2006

A Survey of Merger Remnants III: Are Merger Remnants Supported by Rotation or Anisotropy

A growing body of observational evidence suggests that the luminosity, photometric shape and amount of rotational or anisotropical support in elliptical galaxies may provide vital clues to how they formed. Elliptical galaxies appear to fall into two distinct categories based on these parameters: bright, boxy shaped, with little or no rotation, and less luminous, disky shaped with significant rotation. One viable formation scenario is the ``Merger hypothesis,'' in which two disk galaxies merge to form a new elliptical galaxy. A comparison of the luminosity, photometric shape, and amount of rotation in advanced merger remnants may shed more light on the possible formation scenarios of elliptical galaxies. Yet, little observational data exists for such merger remnants. This paper is the third in a series investigating the photometric and kinematic properties of a sample of 51 optically selected advanced merger remnants. Presented here are K-band isophotal shapes and spatially resolved kinematics for a sub-sample of 37 merger remnants. The results show that ~ 11% of the sample are boxy, and anisotropically supported while ~ 47% are disky, and rotationally supported. The remainder of the sample show variations among expected correlations between shape and rotation. This may suggest that the isophotal shapes are still ``in flux.'' There does appear to be a lower limit to the amount of anisotropy observed in the merger remnants. This may provide an observational diagnostic for discriminating among formation scenarios in elliptical galaxies.

astro-ph↗

arXiv2005

A Survey of Merger Remnants II: The Emerging Kinematic and Photometric Correlations

This paper is the second in a series exploring the properties of 51 {\it optically} selected, single-nuclei merger remnants. Spectroscopic data have been obtained for a sub-sample of 38 mergers and combined with previously obtained infrared photometry to test whether mergers exhibit the same correlations as elliptical galaxies among parameters such as stellar luminosity and distribution, central stellar velocity dispersion ($\sigma$$_{\circ}$), and metallicity. Paramount to the study is to test whether mergers lie on the Fundamental Plane. Measurements of $\sigma$$_{\circ}$ have been made using the Ca triplet absorption line at 8500 {\AA} for all 38 mergers in the sub-sample. Additional measurements of $\sigma$$_{\circ}$ were made for two of the mergers in the sub-sample using the CO absorption line at 2.29 $\micron$. The results indicate that mergers show a strong correlation among the parameters of the Fundamental Plane but fail to show a strong correlation between $\sigma$$_{\circ}$ and metallicity (Mg$_{2}$). In contrast to earlier studies, the $\sigma$$_{\circ}$ of the mergers are consistent with objects which lie somewhere between intermediate-mass and luminous giant elliptical galaxies. However, the discrepancies with earlier studies appears to correlate with whether the Ca triplet or CO absorption lines are used to derive $\sigma$$_{\circ}$, with the latter almost always producing smaller values. Finally, the photometric and kinematic data are used to demonstrate for the first time that the central phase-space density of mergers are equivalent to elliptical galaxies. This resolves a long-standing criticism of the merger hypothesis.

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arXiv1999

The Correlation Between Galaxy HI Linewidths and K' Luminosities

The relationship between galaxy luminosities and rotation rates is studied with total luminosities in the K' band. Extinction problems are essentially eliminated at this band centered at 2.1 micron. A template luminosity-linewidth relation is derived based on 65 galaxies drawn from two magnitude-limited cluster samples. The zero-point is determined using 4 galaxies with accurately known distances. The calibration is applied to give the distance to the Pisces Cluster (60 Mpc) at a redshift in the CMB frame of 4771 km/s. The resultant value of the Hubble Constant is 81 km/s/Mpc. The largest sources of uncertainty arises from the small number of zero-point calibrators at this time at K' and present application to only one cluster.

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