Minkowski's Object Research Articles

Observations and Simulations of Radio Emission and Magnetic Fields in Minkowski's Object

We combine new data from the Karl G. Jansky Very Large Array with previous radio observations to create a more complete picture of the ongoing interactions between the radio jet from galaxy NGC 541 and the star-forming system known as Minkowski’s Object (MO). We then compare those observations with synthetic radio data generated from a new set of magnetohydrodynamic simulations of jet–cloud interactions specifically tailored to the parameters of MO. The combination of radio intensity, polarization, and spectral index measurements all convincingly support the interaction scenario and provide additional constraints on the local dynamical state of the intracluster medium and the time since the jet–cloud interaction first began. In particular, we show that only a simulation with a bent radio jet can reproduce the observations.

ALMA Observations of the Interaction of a Radio Jet with Molecular Gas in Minkowski's Object

Abstract We use the Atacama Large Millimeter Array (ALMA) to detect and image CO (1-0) emission from Minkowski’s Object, a dwarf galaxy in the cluster Abell 194 that is interacting with a radio jet from a nearby elliptical galaxy. The ALMA observations, which are the first to detect molecular gas in Minkowski’s Object, also image the high-frequency continuum emission from the radio jet, allowing us to study the interaction in detail. We estimate the range in the mass of molecular gas in Minkowski’s Object assuming two different values of the ratio of the molecular gas mass to the CO luminosity, . For the Milky Way value of we obtain a molecular gas mass of , 6% of the H I gas mass. We also use the prescription of Narayanan et al. (2012) to estimate an , in which case we obtain , 36% of the H I mass. The observations are consistent with previous claims of star formation being induced in Minkowski’s Object via the passage of the radio jet, and it therefore being a rare local example of positive feedback from an active galactic nucleus. In particular, we find highly efficient star formation, with gas depletion timescales year (for assumed values of and , respectively) in the upstream regions of Minkowski’s Object that were struck first by the jet, and less efficient star formation downstream. We discuss the implications of this observation for models of jet-induced star formation and radio-mode feedback in massive galaxies.

Further evidence for a quasar-driven jet impacting its neighbour galaxy: The saga of HE0450-2958 continues

HE0450-2958, an interacting quasar-starburst galaxy pair at $z$ = 0.285, is one of the best known examples of strong star formation activity in the presence of a quasar-driven jet. We present new multi-band JVLA-imaging covering 1 to 6 GHz and reaching an angular resolution of up to $0{}_{{}^.}^{"}6$ (a 6-fold improvement over existing radio data). We confirm the previous detection of a spatially extended radio component around the quasar indicating that there is on-going star formation activity in the quasar host galaxy. For the first time, we directly detect a jet-like bipolar outflow from the quasar aligned with its companion star-forming galaxy (SFG) and several blobs of ionized gas in its vicinity identified in previous studies. Within the companion SFG we find evidence for a flattening of the synchrotron spectral index towards the point of intersection with the jet axis, further suggesting that the outflow may actually be impacting its interstellar medium (ISM). We discuss two possible mechanisms that could have triggered the starburst in the companion SFG: a wet-dry merger with the quasar and jet-induced star formation. While triggering through interaction-driven gas dynamics cannot be excluded with current data, our new observations make HE0450-2958 a strong candidate for jet-induced star formation, and one of the rare links between local systems (like Minkowski's Object or Centaurus A) and the high-z regime where radio-optical alignments suggest that this phenomenon could be more common.

Jet-induced star formation in 3C 285 and Minkowski’s Object

How efficiently star formation proceeds in galaxies is still an open question. Recent studies suggest that AGN can regulate the gas accretion and thus slow down star formation (negative feedback). However, evidence of AGN positive feedback has also been observed in a few radio galaxies (eg. Centaurus A). Here we present CO observations of 3C 285 and Minkowski Object (MO), which are examples of jet-induced star formation. A spot (named 09.6) aligned with the 3C 285 radio jet, at a projected distance of ~70 kpc from the galaxy centre, shows star formation, detected in optical emission. MO is located along the jet of NGC 541 and also shows star formation. To know the distribution of molecular gas along the jets is a way to study the physical processes at play in the AGN interaction with the intergalactic medium. We observed CO lines in 3C 285, NGC 541, 09.6 and MO with the IRAM-30m telescope. In the central galaxies, the spectra present a double-horn profile, typical of a rotation pattern, from which we are able to estimate the molecular gas density profile of the galaxy. The molecular gas appears to be in a compact reservoir. In addition, no kinematic signature of a molecular outflow is detected by the 30m-telescope. Interestingly, 09.6 and MO are not detected in CO. The cold gas mass upper limits are consistent with a star formation induced by the compression of dense ambient material by the jet. The depletion time scales are of the order of and even smaller than what is found in 3C 285, NGC 541 and local spiral galaxies (10^9 yr). The molecular gas surface density in 09.6 follows a Schmidt-Kennicutt law if the emitting region is very compact, while MO is found to have a much higher SFE (very short depletion time). Higher sensitivity and spatial resolution are necessary to detect CO in the spots of star formation, and map the emission in these jet-induced star forming regions.

CHANDRAANDROSATOBSERVATIONS OF A194: DETECTION OF AN X-RAY CAVITY AND MAPPING THE DYNAMICS OF THE CLUSTER

Based on Chandra and ROSAT observations, we investigated the nearby poor cluster Abell 194, which hosts two luminous radio galaxies, NGC547 (3C 40B) and NGC541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r~34 kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC547. The estimated age of the cavity is t=7.9 x 10^7 years and the total work of the AGN is 3.3 x 10^59 erg, hence the cavity power is P_cav=1.3 x 10^44 erg/s. Furthermore, in the Chandra images of NGC545 and NGC541 we detected sharp surface brightness edges, identified as merger cold fronts, and extended tails. Using the pressure ratios between inside and outside the cold fronts we estimated that the velocities of NGC545 and NGC541 correspond to Mach-numbers of M=1.0^{+0.3}_{-0.5} and M=0.9^{+0.2}_{-0.5}, respectively. The low radial velocities of these galaxies relative to the mean radial velocity of Abell 194 imply that their motion is oriented approximately in the plane of the sky. Based on these and earlier observations, we concluded that NGC545 and NGC541 are falling through the cluster, whose center is NGC547, suggesting that Abell 194 is undergoing a significant cluster merger event. Additionally, we detected 20 bright X-ray sources around NGC547 and NGC541, a surprisingly large number, since the predicted number of resolved LMXBs and CXB sources is 2.2 and 4.1, respectively. To explain the nature of additional sources, different possibilities were considered, none of which are satisfactory. We also studied the origin of X-ray emission in Minkowski's Object, and concluded that it is most likely dominated by the population of HMXBs rather than by hot diffuse ISM. Moreover, in view of the galaxy dynamics in Abell 194, we explored the possibility that the starburst in Minkowski's Object was triggered by its past interaction with NGC541, and concluded that it may be a viable path.

Minkowski’s Object: A Starburst Triggered by a Radio Jet, Revisited

We present neutral hydrogen, ultraviolet, optical, and near-infrared imaging, and optical spectroscopy, of Minkowski's Object (MO), a star-forming peculiar galaxy near NGC 541. The observations strengthen evidence that star formation in MO was triggered by the radio jet from NGC 541. Key new results are the discovery of a 4.9 × 10^8 M_⊙ double H I cloud straddling the radio jet downstream from MO, where the jet changes direction and decollimates; strong detections of MO, also showing double structure, in UV and Hα; and numerous H II regions and associated clusters in MO. In UV, MO resembles the radio-aligned, rest-frame UV morphologies in many high-redshift radio galaxies (HzRGs), also thought to be caused by jet-induced star formation. MO's stellar population is dominated by a 7.5 Myr old, 1.9 × 10^7 M_⊙ instantaneous burst, with a current star formation rate of 0.52 M_⊙ yr^(-1) (concentrated upstream from where the H I column density is high). This is unlike the jet-induced star formation in Centaurus A, where the jet interacts with preexisting cold gas; in MO, the H I may have cooled out of a warmer, clumpy intergalactic or interstellar medium as a result of jet interaction, followed by the collapse of the cooling clouds and subsequent star formation (consistent with numerical simulations). Since the radio source that triggered star formation in MO is much less luminous, and therefore more common than powerful HzRGs, and because the environment around MO is not particularly special in terms of abundant dense, cold gas, jet-induced star formation in the early universe might be even more prevalent than previously thought.

Radiative Shock–induced Collapse of Intergalactic Clouds

Accumulating observational evidence for a number of radio galaxies suggests an association between their jets and regions of active star formation. The standard picture is that shocks generated by the jet propagate through an inhomogeneous medium and trigger the collapse of overdense clouds, which then become active star-forming regions. In this contribution, we report on recent hydrodynamic simulations of radiative shock-cloud interactions using two different cooling models: an equilibrium cooling-curve model assuming solar metallicities and a nonequilibrium chemistry model appropriate for primordial gas clouds. We consider a range of initial cloud densities and shock speeds in order to quantify the role of cooling in the evolution. Our results indicate that for moderate cloud densities (≳1 cm-3) and shock Mach numbers (≲20), cooling processes can be highly efficient and result in more than 50% of the initial cloud mass cooling to below 100 K. We also use our results to estimate the final H2 mass fraction for the simulations that use the nonequilibrium chemistry package. This is an important measurement, since H2 is the dominant coolant for a primordial gas cloud. We find peak H2 mass fractions of ≳10-2 and total H2 mass fractions of ≳10-5 for the cloud gas, consistent with cosmological simulations of first star formation. Finally, we compare our results with the observations of jet-induced star formation in "Minkowski's Object," a small irregular starburst system associated with a radio jet in the nearby cluster of galaxies Abell 194. We conclude that its morphology, star formation rate (~0.3 M☉ yr-1) and stellar mass (~1.2 × 107 M☉) can be explained by the interaction of a ~9 × 104 km s-1 jet with an ensemble of moderately dense (~10 cm-3), warm (104 K) intergalactic clouds in the vicinity of its associated radio galaxy at the center of the galaxy cluster.

Jet-Induced Star Formation

Jets from radio galaxies can have dramatic effects on the medium through which they propagate. We review observational evidence for jet-induced star formation in low (‘FR-I’) and high (‘FR-II’) luminosity radio galaxies, at low and high redshifts respectively. We then discuss numerical simulations which are aimed to explain a jet-induced starburst (‘Minkowski's Object’) in the nearby FR-I type radio galaxy NGC 541. We conclude that jets can induce star formation in moderately dense (10 cm−3), warm (104 K) gas; that this may be more common in the dense environments of forming, active galaxies; and that this may provide a mechanism for ‘positive’ feedback from AGN in the galaxy formation process.

The origin of the optical emission lines associated with extragalactic radio sources

The observed extended emission line regions (EELRs) associated with radio sources are investigated with the objective of determining the characteristics of the ionization mechanisms and the possible effect of star formation. The sources included in the sample are 3C 227, 3C 277.3, 3C 305, Cen A (NGC 5128), NGC 7385, PKS 0349-27, PKS 2152-69, and Minkowski's Object. It is shown that the emission-line ratios of the EELRs considered can be explained by models which account for the coupled effect of photoionization and shock acting at different degrees. It is also shown that the EELR ionization is not due to young stars. The main energy sources of the EELR are identified.

Extended optical line emission associated with radio galaxies

Observations of radio galaxies that have extended optical emission-line regions provide a new way of studying the interaction of extragalactic jets with their ambient medium. Their general properties are briefly reviewed and are illustrated using recent results on 4C 29.30 and Minkowski's Object.

Extragalactic jets and their interaction with their environment

We describe three optical observational projects, each carried out in conjunction with studies at other wavelengths. These emphasize the usefulness of multifrequency studies in elucidating the nature of extragalactic jets. The first part concerns regions of optical line and continuum emission found at the sites of X-ray-radio knots in the inner 2 kpc of the Centaurus A jet. We show that these regions are physically associated with the jet and cite evidence for shock excitation within the emitting clumps. The full-spectrum continuum emission is attributed to the synchrotron process. Next we report the preliminary results of a search for optical emission in the fields of five radio jets. In the field of Abell 194 we find evidence for a jet-galaxy interaction. The optical-emission region known as Minkowski's Object is found to lie in the path of a radio jet. Spectroscopic investigation supports the view that it results from a burst of star formation, triggered by the impact of the jet on a cloud of material in its path. Last, we describe simultaneous multifrequency observations of the highly variable BL Lac object Mkn421. Dramatic changes in X-ray flux on time scales of weeks are not reproduced at other wavelengths. The X-ray variations are such that the lowest energy photons undergo the least change. These results allow some discrimination between the various theoretical jet models that have been proposed to describe the properties of BL Lacs. We also discuss possible interpretations for shorter time-scale (~10 000 s) variations with 10% amplitude, which were observed in X-ray light curves when the source was in an X-ray bright state.

Environnement du noyau de 3C 120

The region surrounding the nucleus of 3C 120 has been recorded on electronographic plates, in U, B, V and V' colours. It has been possible to substract the contributions of the bright nucleus and the galaxy. Faint condensations appear. Their colours show that they are probably not emitting synchrotron radiation. The brightest condensation A is located 4” West of the nucleus. It does not coïncide exactly with the knot of the radio jet and is very slightly displaced toward the North. It is probably of the same nature as Minkowski's Object: burst of star formation triggered by the collision of the jet with relatively dense extranuclear gas.

Minkowski's object - A starburst triggered by a radio jet

New radio and optical images of Minkowski's object, a peculiar blue object near the elliptical galaxy NGC 541 in the cluster Abell 194, are presented. The observations show that the object is a region with bright optical line and continuum emission which are morphologically related and associated with a radio jet emanating from NGC 541. Optical emission is brightest near the edges of the jet, correlated with the absence of polarized radio emission, and filamentary downstream where the radio jet is deflected and decollimated. Minkowski's object exhibits unusually bright optical continuum emission, and its spectrum resembles those of galaxies dominated by giant H II regions. Observations of the prototypical starburst galaxy NGC 7714 (Weedman et al., 1981) confirm that the optical emission from Minkowski's object is caused by the photoionization of gas by type O and B stars. 71 references.

Optical Properties of the Radio Source PKS 0123-01 (3C 40) in Abell 194

view Abstract Citations (18) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Properties of the Radio Source PKS 0123-01 (3C 40) in Abell 194 Simkin, S. M. Abstract An optical bridge between the radio galaxies NOC 547/545 and NOC 541 in A194 is found to have a B - V color and continuous spectrum which resemble those for stars in the outer regions of elliptical galaxies. Embedded in this bridge is a peculiar galaxy ("Minkowski's object") which is also a radio source. Its red shift is compatible with cluster membership. Its absolute magnitude, UBV colors, and, in some respects, its emission-line spectrum, are similar to those of the metalpoor, isolated extragalactic H ii regions sometimes associated with elliptical galaxies. In other respects, however, its optical spectrum is similar to that of the radio galaxies Cyg A and 3C 390.3, exhibiting a steep Balmer decrement, high excitation lines of [Ne v] and He ii, and a low ratio of [0 iii] (N1 + N2):A4363. Subject headings: galaxies: clusters of - radio sources: general Publication: The Astrophysical Journal Pub Date: February 1976 DOI: 10.1086/154166 Bibcode: 1976ApJ...204..251S full text sources ADS | data products NED (4)