arXiv subjects

Roger Coziol

Publications and source records attributed to Roger Coziol.

At least 19 recordsLinked to original sources

arXiv2026

A new solution for the mass growth of Black Holes consistent with thermodynamics

The James Webb Space Telescope (JWST) has recently revealed evidence of supermassive black holes (SMBHs) forming in the cores of high redshift galaxies that grew in mass extremely rapidly during the first billion years of the universe. In this study we present a new solution where the growth mass factor of BHs, $\gamma(t) \propto \dot M_{BH}/M_{BH}$, varies with time, following the changes of radiative efficiency, $\epsilon$, and Eddington ratio, $\lambda_{Edd}$, caused by the variation in accretion flow. By optimizing the accretion rate, $\dot M_{BH}$, we obtained a solution that is universal, that is, which applies to any BH at any redshift. This suggests that the mass of the BH is a thermodynamics state function, in good agreement with the no hair theorem and the four laws of mechanics of BHs.

astro-ph.GA↗

arXiv2025

Testing the AGN Paradigm, Part I: a generic SED for Seyfert 1 galaxies

This article presents the first part of a study aimed at testing the unification paradigm for AGN (UPAGN) using the SED reconstruction code X-CIGALE. Our method consists in obtaining a generic SED for a large sample of Seyfert 1 (Sy1; part 1), then applying this SED to Seyfert 2 (Sy2; Part~II), expecting that the only difference will be the line-of-sight (LOS) angle, $i$, relative to the polar axis of the torus of gas and dust obscuring the broad line regions (BLRs). Our sample is composed of 3,896 Type 1, Sy1 at low redshifts, $ z<0.4$, separated into four spectral subgroups depending on the presence or absence in their spectra of narrow emission lines, Sy1N/Sy1B, and AGN wind, Sy1Bw and Sy1Nw. The generic SED produced by X-CIGALE applies to 90\% of the Sy1 in our sample. It includes a clumpy torus with an AGN engine seen face-on ($i \sim 10^\circ \pm 5^\circ$). Our analysis not only supports the existence of a torus in Sy1, in good agreement with UPAGN, but also reveals new facts about the accretion of matter and AGN wind: 1- a sudden accretion of matter from the BLR to the accretion disk triggered the wind, 2- matter from the wind replenishes the torus, consistent with a gradual formation of this structure by recurrent AGN winds, and 3- Sy1Bw and Sy1Nw eventually evolve as AGN without wind, leaving behind a torus as evidence of a higher AGN activity in their past.

astro-ph.GA↗

arXiv2024

The role of AGN winds in galaxy formation: connecting AGN outflows at low redshifts to the formation/evolution of their host galaxies

Using SDSS spectra, we applied an automatic method to search for outflows (OFs) in three large samples of narrow-line AGN at low redshifts (z < 0.4), separated in three spectral activity classes: radio-loud RG, 15,793, radio-quiet, Sy2, 18,585, and LINER, 25,656. In general, the probability of detecting an OF decreases along the sequence Sy1->Sy2->LINER/RG and, independently of the AGN class, the wind velocity, traced by W80, increases with the AGN luminosity. Moreover W80 is systematically higher in RG or any of the other AGN class when detected in radio. These results support the idea that there are two main modes of production of OF, the radiative mode dominant in radio-quiet AGN and the jet mode dominant in radio-loud galaxies, although both modes could also happen simultaneously at different levels. From the spectra and SDSS photometry, the characteristics of the AGN host galaxies and their super-massive black holes (SMBHs) were also retrieved using the stellar population synthesis code STARLIGHT. This revealed that, independently of their spectral class, 1) galaxy hosts with OFs have systematically later morphological types and higher star formation rates than their counterpart without OF, 2) they occupy different positions in the specific diagnostic diagram, sSMBH vs. sSFR, which suggests they follow different evolutionary paths congruent with the morphology of their galaxy hosts, and 3) they show no evidence of AGN quenching or triggering of star formation. These results are consistent with a scenario explaining the different AGN classes as consequences of different formation processes of galaxies: early-type galaxies (LINER and RG) formed bigger bulges and more massive SMBHs, exhausting their reservoir of gas more rapidly than late-type galaxies (Sy2 and Sy1), quenching their star formation and starving their SMBHs.

astro-ph.GA↗

arXiv2023

Tracing the assembly histories of galaxy clusters in the nearby universe

We have compiled a sample of 67 nearby ($z$ < 0.15) clusters of galaxies, for which on average more than 150 spectroscopic members are available, and, by applying different methods to detect substructures in their galaxy distribution, we have studied their assembly history. Our analysis confirms that substructures are present in 70% of our sample, having a significant dynamical impact in 57% of them. A classification of the assembly state of the clusters based on the dynamical significance of their substructures is proposed. In 19% of our clusters, the originally identified brightest cluster galaxy is not the central gravitationally dominant galaxy (CDG), but turns out to be either the second-rank, or the dominant galaxy of a substructure (a SDG, in our classification), or even a possible "fossil" galaxy in the periphery of the cluster. Moreover, no correlation was found in general between the projected offset of the CDG from the X-ray peak and its peculiar velocity. The comparison of the CDGs properties with the assembly states and dynamical state of the intracluster media, especially the core cooling status, suggests a complex assembly history, with clear evidence of co-evolution of the CDG and its host cluster in the innermost regions.

astro-ph.CO↗

arXiv2023

Probing the rapid formation of black holes and their galaxy hosts in QSOs

Using the modelling code X-CIGALE, we reproduced the SEDs of 1,359 SDSS QSOs within the redshift range 0 < z < 4, for which we have NIR/MIR fluxes with the highest quality and spectral data characterizing their SMBHs. Consistent with a rapid formation of the host galaxies, the star formation histories (SFHs) have small e-folding, at most 750 Myrs using an SFH function for Spiral or 1000 Myrs using one for Elliptical. Above z \sim 1.6, the two solutions are degenerate, the SEDs being dominated by the AGN continuum and high star formation rates (SFRs), typical of starburst galaxies, while at lower redshifts the starburst nature of the host, independent from its morphology, is better reproduced by an Spiral SFH. In general, the SFR increases with the redshift, the mass of the bulge, the AGN luminosity and Eddington ratio, suggesting there is no evidence of AGN quenching of star formation. Comparing the specific BHAR with specific SFR, all the QSOs at any redshift trace a linear sequence below the Eddington luminosity, in parallel and above the one-to-one relation, implying that QSOs are in a special phase of evolution during which the growth in mass of their SMBH is more rapid than the growth in mass of their galaxy hosts. This particular phase is consistent with a scenario where the galaxy hosts of QSOs in the past grew in mass more rapidly than their SMBHs, suggesting that a high star formation efficiency during their formation was responsible in limiting their masses

astro-ph.GA↗

arXiv2020

The ubiquity of AGN winds in Seyfert 1 galaxies at low redshift

The optical spectra of 3,896 Seyfert~1 (Sy1) galaxies detected with WISE at z < 0.4 were analyzed for evidence of outflows. In 37% of the Sy1s the outflows appear as broad, blue-shifted, of the [OIII]5007, with a mean maximum velocity V_max ~1014 km/s$, consistent with AGN winds. For each Sy1 we deduced that black hole (BH) mass, bolometric luminosity, Eddington ratio and power-law index of the continuum, which we compared with the star formation rate (SFR) and host morphology. Having separated our sample in two spectroscopic subgroups, Sy1s with only broad Balmer lines (Sy1B) and with both narrow and broad (Sy1N) lines and distinguishing those that show as outflow (Sy1Bw and Sy1Nw), we report the following differences: 1) the BH mass is systematically higher and the power-law steeper in the Sy1B-Sy1Bw than in the Sy1N-Sy1Nw, 2) V_max is higher in the Sy1Bw than in the Sy1Nw, correlated in both groups with the BH mass and bolometric luminosity, 3) the Eddington ratio and SFR are higher in the Sy1 with outflows, and 4) the specific star formation rates (sSFRs) of the Sy1s are normal for their morphology and mass; typical of early-type spiral galaxies in the green valley, far from the quenched regime. From these results we conclude that in Sy1s AGN winds are triggered by higher accretion rates and probably radiatively launched, and there is no clear evidence of an effect on the star formation.

astro-ph.GA↗

arXiv2016

What sparks the radio-loud phase of nearby quasars?

To better constrain the hypotheses proposed to explain why only a few quasars are radio loud (RL), we compare the characteristics of 1958 nearby $(z\le 0.3)$ SDSS quasars, covered by the FIRST and NVSS radio surveys. Only 22\% are RL with $\log(L_{1.4{\rm GHz}}) \ge 22.5$ W Hz$^{-1}$, the majority being compact (C), weak radio sources (WRS), with $\log(L_{1.4{\rm GHz}}) < 24.5$ W Hz$^{-1}$. 15\% of the RL quasars have extended radio morphologies: 3\% have a core and a jet (J), 2\% have a core with one lobe (L), and 10\% have a core with two lobes (T), the majority being powerful radio sources (PRS), with $\log(L_{1.4{\rm GHz}}) \ge 24.5$ W Hz$^{-1}$. In general, RL quasars have higher bolometric luminosities and ionisation powers than radio quiet (RQ) quasars. The WRS have comparable black hole (BH) masses as the RQ quasars, but higher accretion rates or radiative efficiencies. The PRS have higher BH masses than the WRS, but comparable accretion rates or radiative efficiencies. The WRS also have higher $FWHM_{\rm [OIII]}$ than the PRS, consistent with a coupling of the spectral characteristics of the quasars with their radio morphologies. Inspecting the SDSS images and applying a neighbour search algorithm reveal no difference between the RQ and RL quasars of their host galaxies, environments, and interaction. Our results prompt the conjecture that the phenomenon that sparks the radio-loud phase in quasars is transient, intrinsic to the AGN, and stochastic, due to the chaotic nature of the accretion process of matter onto the BHs.

astro-ph.GA↗

arXiv2016

Relation between Brown Dwarfs and Exoplanets

One of the most debated subjects in Astronomy since the discovery of exoplanets is how can we distinguish the most massive of such objects from very-low mass stars like Brown Dwarfs (BDs)? We have been looking for evidences of a difference in physical characteristics that could be related to different formation processes. Using a new diagnostic diagram that compares the baryonic gravitational potential (BGP) with the distances from their host stars, we have classified a sample of 355 well-studied exoplanets according to their possible structures. We have then compared the exoplanets to a sample of 87 confirmed BDs, identifying a range in BGP that could be common to both objects. By analyzing the mass-radius relations (MRR) of the exoplanets and BDs in those different BGP ranges, we were able to distinguish different characteristic behaviors. By comparing with models in the literature, our results suggest that BDs and massive exoplanets might have similar structures dominated by liquid metallic hydrogen (LMH).

astro-ph.EP↗

arXiv2004

The Relation of Compact Groups of Galaxies with Larger-scale Structures

We show that Compact Groups of Galaxies (CGs) are frequently associated with larger-scale structures, and such associations become more frequent for CGs selected by the same criteria at higher redshifts. Our findings suggest that CGs are an intrinsic part of the cosmological structure formation process and are consistent with the LambdaCDM (or "concordance") model, but only if galaxy formation is a biased process.

astro-ph↗

arXiv2004

The relation between galaxy activity and the dynamics of compact groups of galaxies

Using a sample of 91 galaxies distributed over 27 Compact Groups of Galaxies (CGs), we define an index that allows us to quantify their level of activity, be it AGN or star formation. By combining the mean activity index with the mean morphological type of the galaxies in a group we are able to quantify the evolutionary state of the groups. We find that they span a sequence in evolution, which is correlated with the spatial configuration of the galaxies making up a CG. We distinguish three main configuration: Type A CGs show predominantly low velocity dispersions and are rich in late-type spirals that are active in terms of star formation or harbor an AGN; Type B groups have intermediate velocity dispersions and contain a large fraction of interacting or merging galaxies; Type C is formed by CGs with high velocity dispersions, which are dominated by elliptical galaxies that show no activity. We suggest that the level of evolution increases in the sense A-->B-->C. Mapping the groups with different evolution levels in a diagram of radius versus velocity dispersion does not reveal the pattern expected based on the conventional fast merger model for CGs. Instead, we observe a trend that goes contrary to expectation: the level of evolution of a group increases with velocity dispersion. This trend seems to be related to the masses of the structures in which CGs are embedded. In general, the level of evolution of a group increases with the mass of the structure. This suggests either that galaxies evolve more rapidly in massive structures or that the formation of CGs embedded in massive structures predated the formation of CGs associated with lower mass systems. Our observations are consistent with CDM (or Lambda CDM) structures formation scenarios, assuming the formation of galaxies is a biased process.

astro-ph↗

arXiv2003

The PDS vs. Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12$μ$m and 25$μ$m in the nearby universe

(Abridged) The characteristics of the starburst galaxies from the Pico dos Dias survey (PDS) are compared with those of the nearby UV-bright Markarian starburst galaxies, having the same limit in redshift ($v_h < 7500$ km s$^{-1}$) and absolute $B$ magnitude ($M_B < -18$). An important difference is found: the Markarian galaxies are generally undetected at 12$μ$m and 25$μ$m in \textit{IRAS}. This is consistent with the UV excess shown by these galaxies and suggests that the youngest star forming regions dominating these galaxies are relatively free of dust. The FIR selection criteria for the PDS is shown to introduce a strong bias towards massive (luminous) and large size late-type spiral galaxies. This is contrary to the Markarian galaxies, which are found to be remarkably rich in smaller size early-type galaxies. These results suggest that only late-type spirals with a large and massive disk are strong emitter at 12$μ$m and 25$μ$m in \textit{IRAS} in the nearby universe.

astro-ph↗

arXiv2000

The Relation Between Activity and Environment in Compact Groups of Galaxies

We present the results of the classification of spectral activity types for 193 galaxies from a new sample of 49 compact groups of galaxies in the southern hemisphere (SCGs). This sample was selected in automated fashion from a digitized galaxy catalogue, covering an area of ~5200 sq deg, around the South Galactic Pole. It is complete up to m ~14.5 in b_j for the brightest galaxy of the group. The spectral analysis of the SCG galaxies confirms the results previously obtained for a smaller sample of Hickson's compact groups (HCG). We confirm the luminosity-activity and morphology-activity relations, as well as the predominance of AGNs (41% of SCGs galaxies). We verified also that the number of early-type non-emission-line galaxies increases with the number of members in the group. The SCGs contain more star-forming galaxies (SFGs) and less non-emission-line galaxies than HCGs, which suggests that they probe a wider range of physical properties. The SFGs are composed in majority of HII Nucleus Galaxies, which have less intense star formation than starburst galaxies. The star formation activity in SCGs is, consequently, remarkably low. The SFGs show also evidence for nuclear activity. If these results are further confirmed, 70% of the galaxies in SCGs would then have an active nucleus, making these systems remarkably rich in AGNs. Curiously, however, this characteristic of CGs generally excludes Seyfert 1 galaxies.(Abridged)

astro-ph↗

arXiv1999

HCG 16 Revisited: Clues About Galaxy Evolution in Groups

We present new spectroscopic observations of 5 galaxies, members of the unusually active compact group HCG 16, observed using the Palomar 5m telescope. The high signal to noise ratios (S/N $\sim 70$) of the spectra allow us to study the variation of the emission line characteristics and the stellar populations in the nucleus and the circumnuclear regions of the galaxies. The emission line characteristics of these galaxies are complex, varying between Seyfert 2 and LINERs or between LINERs and starbursts. All of the galaxies show traces of intermediate age stellar populations, supporting our previous result that post-starburst galaxies are common in compact groups. The galaxies HCG16--4 and HCG16--5 show double nuclei and therefore could be two cases of recent merger. Our observations support a scenario where HCG 16 was formed by the successive merger of metal poor, low mass galaxies. The galaxies HCG16--1 and HCG16--2, which are more evolved, form the old core of the group. Galaxies HCG16--4 and HCG16--5 are two more recent additions still in a merging phase. Galaxy HCG16--5 is a starburst galaxy which is just beginning to fall into the core. If HCG 16 is representative of compact groups in their early stage, the whole set of observations implies that the formation of compact groups is the result of hierarchical galaxy formation. HCG 16 could be one example of this process operating in the local universe.

astro-ph↗

arXiv1998

The Evolution of Galaxies in Compact Groups

We present the analysis of the spectra of 62 galaxies in 15 compact groups. The galaxies were classified in four activity classes: galaxies without emission, starburst nucleus galaxies (SBNGs), luminous AGNs and low-luminosity AGNs (LLAGNs). The star formation in the HCG starbursts is more intense than in normal spirals, but comparable to those in the field SBNGs. Their mean gas metallicity is solar and they do not follow the metallicity-luminosity relation traced by the early-type SBNGs in the field, suggesting that most of them are late-type SBNGs. This morphology preference coupled to the observation that the HCG starbursts are predominantly in the halo of the groups is consistent with the idea that compact groups are embedded in sparser structures. The stellar metallicities of the non starburst galaxies are relatively high for their luminosities. In these galaxies the equivalent widths of the metal absorption lines are slightly narrower than normal while the Balmer absorption lines are relatively strong. All these galaxies could be ``post-starburst'' at an advanced stage of evolution. Our observations are supporting a scenario where the core of the groups are slowly collapsing evolved systems embedded in more extended structures (Ribeiro et al. 1998). In the core of the groups, the interactions were more frequent and the galaxies evolved at a more rapid rate than in their halos.

astro-ph↗

arXiv1998

The Massive Nearby SBNGs: Young Galaxies in Formation

We discuss the implications of the recent discovery that Starburst Nucleus Galaxies (SBNGs) have lower oxygen abundances than "normal galaxies" of the same morphological type. Our interpretation of this result is that SBNGs are young galaxies, still in the process of formation. We consider several alternatives, but none of them provides a viable explanation. This new result has important consequences for our understanding of galaxy evolution, as it confirms the scenario of hierarchical formation of galaxies, and explains recent observations of the Hubble Space Telescope.

astro-ph↗

arXiv1997

The Nature of the Activity in Hickson Compact Groups of Galaxies

We present the results of the spectral classification of the 82 brightest galaxies in a sample of 17 compact groups. We verify that the AGNs are preferentially located in the most early-type and luminous galaxies of the groups, as is usually observed in the field. But these AGNs also appear to be systematically concentrated towards the central parts of the groups. Our observations suggest a correlation between activity types, morphologies and densities of galaxies in the compact groups. This is consistent with a scenario in which galaxies of compact groups evolve by interacting with their environment and are currently in a quiet phase of their activity

astro-ph↗

arXiv1997

Discovery of a Luminous Quasar in the Nearby Universe

In the course of the Pico dos Dias survey (PDS), we identified the stellar like object PDS456 at coordinates alpha = 17h 28m 19.796s, delta = -14deg 15' 55.87'' (epoch 2000), with a relatively nearby (z = 0.184) and bright (B = 14.69) quasar. Its position at Galactic coordinates l_II = 10.4deg, b_II = +11.2deg, near the bulge of the Galaxy, may explain why it was not detected before. The optical spectrum of PDS456 is typical of a luminous quasar, showing a broad (FWHM ~ 4000 km/s) H_βline, very intense FeII lines and a weak [OIII]\lambda5007 line. PDS456 is associated to the infrared source IRAS 17254-1413 with a 60 \mum infrared luminosity L_{60} = 3.8 x 10^{45} erg/s. The relatively flat slopes in the infrared (α(25,60) = -0.33 and α(12,25) = -0.78) and a flat power index in the optical (F_ν \propto ν^{-0.72}) may indicate a low dust content. A good match between the position of PDS456 and the position of the X-ray source RXS J172819.3-141600 implies an X-ray luminosity L_x = 2.8 x 10^{44} erg/s. The good correlation between the strength of the emission lines in the optical and the X-ray luminosity, as well as the steep optical to X-ray index estimated (α_{ox} = -1.64) suggest that PDS456 is radio quiet. A radio survey previously performed in this region yields an upper limit for radio power at ~ 5 GHz of ~ 2.6 x 10^{30} erg/s/Hz. We estimate the Galactic reddening in this line-of-sight to be A_B \simeq 2.0, implying an absolute magnitude M_B = -26.7 (using H_0 = 75 km s^{-1} Mpc^{-1} and q_0 = 0). In the optical, PDS456 is therefore 1.3 times more luminous than 3C 273 and the most luminous quasar in the nearby (z \leq 0.3) Universe.

astro-ph↗

arXiv1996

The Montreal Blue Galaxy Survey III. Third list of UV-bright candidates

We present and discuss the latest addition of the Montreal Blue Galaxy (MBG) survey. Inspection of 59 Curtis Schmidt plates resulted in the identification of 135 new UV-bright galaxies with B < 15.5. This brings the total number of MBGs to 469. New results of the $V/V_m$ test show that our survey is complete to B = 14.7. From our most recent spectroscopic follow-up, we confirm the discovery of one new Seyfert 1 galaxy and possibly one new Seyfert 2 galaxy. We confirm also the bias of the MBG survey towards the low-excitation and metal rich Starburst Nucleus Galaxies (SBNGs). The spectral characteristics of the MBGs are similar to those of the infrared luminous IRAS galaxies. As a common characteristic, they show a mean ratio Log([NII]/H$α$) in excess of 0.2 dex as compared to normal disk HII regions. In general, the MBGs have lower far-infrared luminosities ($L_{IR} < 10^{11} L_{\odot}$) and are nearer (z < 0.05) than the luminous IRAS galaxies. The distribution of the morphologies of the MBGs indicates a high number of early-type spirals (Sb and earlier). Nearly half of these galaxies also possess a bar. In our sample, the fraction of galaxies with bars depends on the morphology and increases towards the late-type spirals. However, if we consider only isolated galaxies, the late-type spirals show a clear tendency to be barred. Signs of a recent interaction with neighbor galaxies are obvious only in 24% of our candidates. Although this number is only a lower limit, it is nevertheless sufficiently low to suggest that in a majority of massive galaxies the burst of star formation do not depends solely on dynamical processes.

astro-ph↗