arXiv subjects

Rodrigo Nemmen

Publications and source records attributed to Rodrigo Nemmen.

29 records · Page 2Linked to original sources

arXiv2020

Winds and feedback from supermassive black holes accreting at low rates: Hydrodynamical treatment

Outflows produced by a supermassive black hole (SMBH) can have important feedback effects in its host galaxy. An unresolved question is the nature and properties of winds from SMBHs accreting at low rates in low-luminosity active galactic nuclei (LLAGNs). We performed two-dimensional numerical, hydrodynamical simulations of radiatively inefficient accretion flows onto non spinning black holes. We explored a diversity of initial conditions in terms of rotation curves and viscous shear stress prescriptions, and evolved our models for very long durations of up to $8 \times 10^5 GM/c^3$. Our models resulted in powerful subrelativistic, thermally-driven winds originated from the corona of the accretion flow at distances $10-100 GM/c^2$ from the SMBH. The winds reached velocities of up to $0.01 c$ with kinetic powers corresponding to 0.1-1% of the rest-mass energy associated with inflowing gas at large distances, in good agreement with models of the "radio mode" of AGN feedback. The properties of our simulated outflows are in broad agreement with observations of winds in quiescent galaxies that host LLAGNs, which are capable of heating ambient gas and suppressing star formation.

astro-ph.HE↗

arXiv2020

Gamma-ray observations of low-luminosity active galactic nuclei

The majority of the activity around nearby (z ~ 0) supermassive black holes is found in low-luminosity active galactic nuclei (LLAGN), the most of them being classified as low ionization nuclear emission regions. Although these sources are well studied from radio up to X-rays, they are poorly understood in gamma-rays. In this work we take advantage of the all sky-surveying capabilities of the Large Area Telescope on board Fermi Gamma ray Space Telescope to study the whole Palomar sample of LLAGN in gamma-rays. Precisely, the four radio-brightest LLAGN in the sample are identified as significant gamma-ray emitters, all of which are recognized as powerful Fanaroff-Riley I galaxies. These results suggest that the presence of powerful radio jets is of substantial importance for observing a significant gamma-ray counterpart even if these jets are misaligned with respect to the line of sight. We also find that most of the X-ray-brightest LLAGN do not have a significant gamma-ray and strong radio emission, suggesting that the X-rays come mainly from the accretion flow in these cases. A detailed analysis of the spectral energy distributions (SEDs) of NGC 315 and NGC 4261, both detected in gamma-rays, is provided where we make a detailed comparison between the predicted hadronic gamma-ray emission from a radiatively inefficient accretion flow (RIAF) and the gamma-ray emission from a leptonic jet-dominated synchrotron self-Compton (SSC) model. Both SEDs are better described by the SSC model while the RIAF fails to explain the gamma-ray observations.

astro-ph.HE↗

arXiv2019

Optical characterization of WISE selected blazar candidates

Over the last decade more than five thousand gamma-ray sources were detected by the Large Area Telescope (LAT) on board Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart in lower energies. This motivated the release of new catalogs of gamma-ray counterpart candidates and several follow up campaigns in the last decade. Recently, two new catalogs of blazar candidates were released, they are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDEBLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterized these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing how efficient they are in selecting true blazars. We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. Then we analyzed these spectra to verify the nature of each selected candidate and see which fraction of the catalogs is composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, specially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions. We found that at least ~ 30% of each catalog is composed by confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (~ 58%) and normal galaxies in the case of KDEBLLACS (~ 38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT 4th Point Source Catalog (4FGL) and to find 25 new BL Lac objects.

astro-ph.HE↗

arXiv2019

The Spin of M87*

Now that the mass of the central black hole in the galaxy M87 has been measured with great precision using different methods, the remaining parameter of the Kerr metric that needs to be estimated is the spin a*. We have modeled measurements of the average power of the relativistic jet and an upper limit to the mass accretion rate onto the black hole with general relativistic magnetohydrodynamic models of jet formation. This allows us to derive constraints on a* and the black hole magnetic flux phi. We find a lower limit on M87*'s spin and magnetic flux of a* > 0.4 and phi > 6 in the prograde case, and a* > 0.5 and phi > 10 in the retrograde case, otherwise the black hole is not able to provide enough energy to power the observed jet. These results indicate that M87* has a moderate spin at minimum and disfavor a variety of models typified by low values of phi known as ``SANE'', indicating that M87* prefers the magnetically arrested disk state. We discuss how different estimates of the jet power and accretion rate can impact a* and phi.

astro-ph.HE↗

arXiv2019

Milky Way globular clusters in gamma-rays: analyzing the dynamical formation of millisecond pulsars

Globular clusters (GCs) are evolved stellar systems containing entire populations of millisecond pulsars (MSPs), which are efficient gamma-ray emitters. Observations of this emission can be used as a powerful tool to explore the dynamical processes leading to binary system formation in GCs. In this work, 9 years of Fermi Large Area Telescope data were used to investigate the gamma-ray emission from all GCs in the Milky Way. 23 clusters were found as gamma-ray bright, with 2 of them never having been reported before. It was also found that magnetic braking probably has a smaller impact on the formation rate of binary systems in metal-rich GCs than previously suggested, while a large value for the two-body encounter rate seems to be a necessary condition. The influence of the encounter rate per formed binary was for the first time explored in conjunction with gamma-ray data, giving evidence that if this quantity is very high, binary systems will get destroyed before having time to evolve into MSPs, thus decreasing the total number of MSPs in a GC. No extended emission was found even for clusters whose optical extent is ~0.5 degrees; all of them are point-like sources spatially in agreement with the optical cores of the GCs, supporting previous X-rays results of heavier objects sinking into the clusters' cores via dynamical friction. The possibility of extrapolating these results to ultra-compact dwarf galaxies is discussed, as these systems are believed to be the intermediate case between GCs and dwarf galaxies.

astro-ph.HE↗

arXiv2019

Precessing winds from the nucleus of the prototype Red Geyser?

Super-massive black holes (SMBH) are present at the center of most galaxies, with the related mass accretion processes giving origin to outflows in Active Galactic Nuclei (AGN). It has been presumed that only intense winds from luminous AGN were able to suppress star formation until the discovery of a new class of galaxies with no recent star formation and with the nucleus in a quiescent state showing kpc scale outflows. We used SDSS MaNGA and Gemini Integral Field Spectroscopy of the prototype Red Geyser Akira and found that the orientation of the outflow changes by about 50$^\circ$ from its nucleus to kpc scales. A possible interpretation is that the outflow is produced by a precessing accretion disk due to a misalignment between the orientation of the disk and the spin of the SMBH. The precession of the central source is also supported by a similar change in the orientation of the ionization pattern. Although similar behavior has commonly being reported for collimated relativistic jets, the precession of an AGN wide wind is reported here for the first time, implying on a larger work surface of the wind, which in turn increases the star formation suppression efficiency of the outflow.

astro-ph.GA↗

arXiv2018

Search for QPOs in Perseus with Fermi LAT

We report the analysis of the gamma-ray variability of NGC 1275--the radio galaxy at the center of the Perseus cluster. NGC 1275 has been observed continuously with the Fermi Large Area Telescope over the last nine years. We applied different time-domain analysis methods including Fourier, wavelets and Bayesian methods, in order to search for quasi-periodic oscillations in the gamma-ray emission. We found no evidence for periodicities of astrophysical origin.

astro-ph.HE↗

arXiv2018

The multiwavelength spectrum of NGC 3115: Hot accretion flow properties

NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a low-luminosity active galactic nucleus (LLAGN). X-ray observations of this LLAGN are able to spatially resolve the hot gas within the sphere of gravitational influence of the supermassive black hole. These observations make NGC 3115 an important testbed for black hole accretion theory in galactic nuclei since they constrain the outer boundary conditions of the hot accretion flow. We present a compilation of the multiwavelength spectral energy distribution (SED) of the nucleus of NGC 3115 from radio to X-rays. We report the results from modeling the observed SED with radiatively inefficient accretion flow (RIAF) models. The radio emission can be well-explained by synchrotron emission from the RIAF without the need for contribution from a relativistic jet. We obtain a tight constraint on the RIAF density profile, $ρ(r) \propto r^{-0.73_{-0.02} ^{+0.01}}$, implying that mass-loss through subrelativistic outflows from the RIAF is significant. The lower frequency radio observation requires the synchrotron emission from a nonthermal electron population in the RIAF, similarly to Sgr A*.

astro-ph.GA↗

arXiv2013

Black Hole Jet Unification in the Fermi Era

AGNs and GRBs produce powerful relativistic jets and their central engines share the same basic astrophysical ingredients, despite the vastly different mass scales. Using Fermi and Swift observations, we find evidence that the jets produced by blazars and GRBs follow the same correlation between the gamma-ray luminosity and kinetic power. This result suggests that jet production and energy dissipation mechanisms are remarkably similar over 10 orders of magnitude in jet power, establishing a physical analogy between AGN and GRBs. We discuss the implications of these results and the road ahead.

astro-ph.HE↗

arXiv2013

Probing The Central Engines Of Low-Luminosity Active Galactic Nuclei

I give a brief review of the observational properties of low-luminosity AGNs (LLAGNs). I outline some unresolved issues in the study of LLAGNs, emphasizing the uncertainties in the role of the truncated thin accretion disk, the dusty obscuring torus and the origin of high-energy radiation (X-rays and gamma-rays). I discuss key future directions for progress, focusing on the broadband multiwavelength observations that will help us address these issues and the importance of high-resolution infrared observations.

astro-ph.HE↗

arXiv2011

Spectral Energy Distribution Models for Low-luminosity Active Galactic Nuclei in LINERs

Low-luminosity active galactic nuclei (LLAGNs) represent the bulk of the AGN population in the present-day universe and they trace the low-level accreting supermassive black holes. In order to probe the accretion and jet physical properties in LLAGNs as a class, we model the broadband radio to X-rays spectral energy distributions (SEDs) of 21 LLAGNs in low-ionization nuclear emission-line regions (LINERs) with a coupled accretion-jet model. The accretion flow is modeled as an inner ADAF outside of which there is a truncated standard thin disk. We find that the radio emission is severely underpredicted by ADAF models and is explained by the relativistic jet. The origin of the X-ray radiation in most sources can be explained by three distinct scenarios: the X-rays can be dominated by emission from the ADAF, or the jet, or the X-rays can arise from a jet-ADAF combination in which both components contribute to the emission with similar importance. For 3 objects both the jet and ADAF fit equally well the X-ray spectrum and can be the dominant source of X-rays whereas for 11 LLAGNs a jet-dominated model accounts better than the ADAF-dominated model for the data. The individual and average SED models that we computed can be useful for different studies of the nuclear emission of LLAGNs. From the model fits, we estimate important parameters of the central engine powering LLAGNs in LINERs, such as the mass accretion rate and the mass-loss rate in the jet and the jet power - relevant for studies of the kinetic feedback from jets.

astro-ph.CO↗