Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1993. / Includes bibliographical references (leaves 1-6 of 2nd sequence).

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Context.M 87 is a giant elliptical galaxy located in the centre of the Virgo cluster, which harbours a supermassive black hole of mass 6.4 × 109 M⊙, whose activity is responsible for the extended (80 kpc) radio lobes that surround the galaxy. The energy generated by matter falling onto the central black hole is ejected and transferred to the intra-cluster medium via a relativistic jet and morphologically complex systems of buoyant bubbles, which rise towards the edges of the extended halo. Aims. To place constraints on past activity cycles of the active nucleus, images of M 87 were produced at low radio frequencies never explored before at these high spatial resolution and dynamic range. To disentangle different synchrotron models and place constraints on source magnetic field, age and energetics, we also performed a detailed spectral analysis of M 87 extended radio-halo. Methods. We present the first observations made with the new Low-Frequency Array (LOFAR) of M 87 at frequencies down to 20 MHz. Three observations were conducted, at 15−30 MHz, 30−77 MHz and 116−162 MHz. We used these observations together with archival data to produce a low-frequency spectral index map and to perform a spectral analysis in the wide frequency range 30 MHz–10 GHz. Results. We do not find any sign of new extended emissions; on the contrary the source appears well confined by the high pressure of the intra-cluster medium. A continuous injection of relativistic electrons is the model that best fits our data, and provides a scenario in which the lobes are still supplied by fresh relativistic particles from the active galactic nuclei. We suggest that the discrepancy between the low-frequency radio-spectral slope in the core and in the halo implies a strong adiabatic expansion of the plasma as soon as it leaves the core area. The extended halo has an equipartition magnetic field strength of ≃10 μG, which increases to ≃13 μG in the zones where the particle flows are more active. The continuous injection model for synchrotron ageing provides an age for the halo of ≃40 Myr, which in turn provides a jet kinetic power of 6−10 × 1044 erg s-1.

In this thesis, I use the new generation of radio interferometer along with X-ray observations to investigate the dynamics and energetics of radio-loud active galaxies which are key to understanding AGN feedback and the evolution of galaxies as a whole. I present new JVLA observations of powerful radio source and use innovative techniques to undertake a detailed analysis of JVLA observations of powerful radio galaxies. I compare two of the most widely used models of spectral ageing, the Kardashev-Pacholczyk and Jaffe-Perola models and also results of the more complex, but potentially more realistic, Tribble model. I find that the Tribble model provides both a good fit to observations as well as providing a physically realistic description of the source. I present the first high-resolution spectral maps of the sources and find that the best-fitting injection indices across all models take higher values than has previously been assumed. I present characteristic hot spot advance speeds and compare them to those derived from dynamical ages, confirming that the previously known discrepancy in speed remains present in older radio sources even when ages are determined at high spectral and spatial resolutions. I show that some previously common assumptions made in determining spectral ages with narrow-band radio telescopes may not always hold. I present results from a study of the powerful radio galaxy 3C223 at low frequencies with LOFAR to determine its spectrum on spatially small scales and tightly constrain the injection index, which I find to be consistent with the high values found at GHz frequencies. Applying this new knowledge of the low energy electron population, I perform synchrotron / inverse-Compton model fitting and find that the total energy content of the radio galaxy lobes increases by a factor greater than 2 compared to previous studies. Using this result to provide revised estimates of the internal pressure, I find the northern lobe to be in pressure balance with the external medium and the southern lobe to be overpressured. I go on to present the first large sample investigation of the properties of jets in Fanaroff and Riley type I radio galaxies (FR-I) at X-ray energies based on data from the Chandra archive. I explore relations between the properties of the jets and the properties of host galaxies in which they reside. I find previously unknown correlations to exist, relating photon index, volume emissivity, jet volume and luminosity, and find that the previously held assumption of a relationship between luminosities at radio and X-ray wavelengths is linear in nature when bona fide FR-I radio galaxies are considered. In addition, I attempt to constrain properties which may play a key role in determination of the diffuse emission process. I test a simple model in which large-scale magnetic field variations are primarily responsible for determining jet properties; however, we find that this model is inconsistent with our best estimates of the relative magnetic field strengths in my sample.

Ventos (em inglês outflows) de ampla abertura e larga escala sâo uma característica comum em galáxias ativas, como as galáxias Seyfert. Em sistemas como este, onde buracos negros supermassivos (em inglês super massive black holes, SMBHs) de núcleos galácticos ativos de galáxias (em inglês active galactic nuclei, AGN) coexistem com regiões de formação estelar (em inglês star forming, SF), nâo está claro das observações se o AGN SMBH ou o SF (ou ambos) são responsaveis pela indução desses ventos. Neste trabalho, estudamos como ambos podem influenciar a evolução da galáxia hospedeira e seus outflows, considerando galáxias tipo Seyfert nas escalas de kilo-parsec (kpc). Para este objetivo, estendemos o trabalho anterior desenvolvido por Melioli & de Gouveia Dal Pino (2015), que considerou ventos puramente hidrodinâmicos impulsionados tanto pela SF quanto pelo AGN, mas levando em conta para este último apenas ventos bem estreitos (colimados). A fim de obter uma melhor compreensão da influencia (feedback) desses mecanismos sobre a evolução da galáxia e seus outflows, incluímos também os efeitos de ventos de AGN com maior ângulo de abertura, já que ventos em forma de cone podem melhorar a interação com o meio interestelar da galáxia e assim, empurrar mais gás nos outflows. Além disso, incluímos também os efeitos dos campos magnéticos no vento, já que estes podem, potencialmente, ajudar a preservar as estruturas e acelerar os outflows. Realizamos simulações tridimensionais magneto-hidrodinâmicas (MHD) considerando o resfriamento radiativo em equilíbrio de ionização e os efeitos dos ventos do AGN com dois diferentes ângulos de abertura (0º e 10º) e razões entre a pressão térmica e a pressão magnética beta=infinito, = 300 e 30, correspondentes a campos magnéticos 0, 0,76 micro-Gauss e 2,4 micro-Gauss respectivamente. Os resultados de nossas simulações mostram que os ventos impulsionados pelos produtos de SF (isto é, pelas explosões de supernovas, SNe) podem direcionar ventos com velocidades 100-1000 km s¹, taxas de perda de massa da ordem de 50 Massas solares/ano, densidades de ~1-10 cm-3 e temperaturas entre 10 e 10 K, que se assemelham às propriedades dos denominados absorvedores de calor (em inglês warm absorbers, WAs) e também são compatíveis com as velocidades dos outflows moleculares observadas. No entanto, as densidades obtidas nas simulações são muito pequenas e as temperaturas são muito grandes para explicar os valores observados nos outflows moleculares (que têm n ~150-300 cm³ e T<1000 K). Ventos colimados de AGN (sem a presença de ventos SF) também são incapazes de conduzir outflows, mas podem acelerar estruturas a velocidades muito altas, da ordem de ~10.000 km s¹ e temperaturas T> 10 K, tal como observado em ventos ultra rapidos (em inglês, ultra-fast outflows, UFOs). A introdução do vento de AGN, particularmente com um grande ângulo de abertura, causa a formação de estruturas semelhantes a fontes galácticas. Isso faz com que parte do gás em expansão (que está sendo empurrado pelo vento de SF) retorne para a galáxia, produzindo um feedback \'positivo\' na evolução da galáxia hospedeira. Descobrimos que esses efeitos são mais pronunciados na presença de campos magnéticos, devido à ação de forças magnéticas extras pelo vento AGN, o qual intensifica o efeito de retorno do gás (fallback), e ao mesmo tempo reduz a taxa de perda de massa nos outflows por fatores de até 10. Além disso, a presença de um vento de AGN colimado (0º) causa uma remoção significativa da massa do núcleo da galáxia em poucos 100.000 anos, mas este é logo reabastecido pelo de gás acretante proveniente do meio interestelar (ISM) à medida que as explosões de SNe se sucedem. Por outro lado, um vento de AGN com um grande ângulo de abertura, em presença de campos magnéticos, remove o gás nuclear inteiramente em alguns 100.000 anos e não permite o reabastecimento posterior pelo ISM. Portanto, extingue a acreção de combustível e de massa no SMBH. Isso indica que o ciclo de trabalho desses outflows é de cerca de alguns 100.000 anos, compatível com as escalas de tempo inferidas para os UFOs e outflows moleculares observados. Em resumo, os modelos que incluem ventos de AGN com um ângulo de abertura maior e campos magnéticos, levam a velocidades médias muito maiores que os modelos sem vento de AGN, e também permitem que mais gás seja acelerado para velocidades máximas em torno de ~10 km s¹, com densidades e temperaturas compatíveis com aquelas observadas em UFOs. No entanto, as estruturas com velocidades intermediárias de vários ~100 km s¹ e densidades até uns poucos 100 cm³, que de fato poderiam reproduzir os outflows moleculares observados, têm temperaturas que são muito grandes para explicar as características observadas nos outflows moleculares, que tem temperaturas T< 1000 K. Além disso, estes ventos de AGN não colimados em presença de campos magnéticos entre T< 1000 K. Alem disso, estes grandes ventos AGN de angulo de abertura em fluxos magnetizados reduzem as taxas de perda de massa dos outflows para valores menores que aqueles observados tanto em outflows moleculares quanto em UFOs. Em trabalhos futuros, pretendemos estender o espaço paramétrico aqui investigado e também incluir novos ingredientes em nossos modelos, como o resfriamento radioativo fora do equilíbrio, a fim de tentar reproduzir as características acima que não foram explicadas pelo modelo atual. / Large-scale broad outflows are a common feature in active galaxies, like Seyfert galaxies. In systems like this, where supermassive black hole (SMBH) active galactic nuclei (AGN) coexist with star-forming (SF) regions it is unclear from the observations if the SMBH AGN or the SF (or both) are driving these outflows. In this work, we have studied how both may influence the evolution of the host galaxy and its outflows, considering Seyfert-like galaxies at kilo-parsec (kpc) scales. For this aim, we have extended previous work developed by Melioli & de Gouveia Dal Pino (2015), who considered purely hydrodynamical outflows driven by both SF and AGN, but considering for the latter only very narrow (collimated) winds. In order to achieve a better understanding of the feedback of these mechanisms on the galaxy evolution and its outflows, here we have included the effects of AGN winds with a larger opening angle too, since conic-shaped winds can improve the interaction with the interstellar medium of the galaxy and thus push more gas into the outflows. Besides, we have also included the effects of magnetic fields in the flow, since these can potentially help to preserve the structures and speed up the outflows. We have performed three-dimensional magneto-hydrodynamical (MHD) simulations considering equilibrium radiative cooling and the effects of AGN-winds with two different opening angles (0º and 10º), and thermal pressure to magnetic pressure ratios of beta=infinite, 300 and 30 corresponding to magnetic fields 0, 0.76 micro-Gauss and 2.4 micro-Gauss, respectively. The results of our simulations show that the winds driven by the products of SF (i.e., by explosions of supernovae, SNe) alone can drive outflows with velocities ~100-1000 km s¹, mass outflow rates of the order of 50 Solar Masses yr¹, densities of ~1-10 cm³, and temperatures between 10 and 10 K, which resemble the properties of warm absorbers (WAs) and are also compatible with the velocities of the observed molecular outflows. However, the obtained densities from the simulations are too small and the temperatures too large to explain the observed values in molecular outflows (which have n ~ 150-300 cm³ and T<1000 K). Collimated AGN winds alone (without the presence of SF-winds) are also unable to drive hese outflows, but they can accelerate structures to very high speeds, of the order of ~ 10.000 km s¹, and temperatures T> 10 K as observed in ultra-fast outflows (UFOs). The introduction of an AGN wind, particularly with a large opening angle, causes the formation of fountain-like structures. This makes part of the expanding gas (pushed by the SF-wind) to fallback into the galaxy producing a \'positive\' feedback on the host galaxy evolution. We have found that these effects are more pronounced in presence of magnetic fields, due to the action of extra magnetic forces by the AGN wind producing enhanced fallback that reduces the mass loss rate in the outflows by factors up to 10. Furthermore, the presence of a collimated AGN wind (0º) causes a significant removal of mass from the core region in a few 100.000 yr, but this is soon replenished by gas inflow from the interstellar medium (ISM) when the SNe explosions fully develop. On the other hand, an AGN wind with a large opening angle in presence of magnetic fields is able to remove the nuclear gas entirely within a few 100.000 yr and does not allow for later replenishment. Therefore, it quenches the fueling and mass accretion onto the SMBH. This indicates that the duty cycle of these outflows is around a few 100.000 yr, compatible with the time-scales inferred for the observed UFOs and molecular outflows. In summary, models that include AGN winds with a larger opening angle and magnetic fields, lead to to be accelerated to maximum velocities around 10 km s¹ (than models with collimated AGN winds), with densities and temperatures which are compatible with those observed in UFOs. However, the structures with intermediate velocities of several ~100 km s¹ and densities up to a few 100 cm3, that in fact could reproduce the observed molecular outflows, have temperatures which are too large to explain the observed molecular features, which have temperatures T<1000 K. Besides, these large opening angle AGN winds in magnetized flows reduce the mass loss rates of the outflows to values smaller than those observed both in molecular outflows and UFOs. In future work, we intend to extend the parametric space here investigated and also include new ingredients in our models, such as non-equilibrium radiative cooling, in order to try to reproduce the features above that were not explained by the current model.

<p>Quasars form one of the most energetic phenomena in the universe, and can be traced out to very large redshifts. By studying the galaxies which host the active nuclei, important insights can be gained into the processes that trigger and maintain the quasar powerhouse. The evolution rate of the quasar population is furthermore similar to that of ordinary galaxies, which implies a connection between black hole accretion and star formation in the host galaxies. While the properties of quasar host galaxies at low redshift have become better constrained in recent years, less is known about hosts at earlier cosmic epochs. In addition, though radio-quiet quasars are by far more common than their radio-loud counterparts their host galaxies have not been studied to the same extent, in particular not at higher redshifts.</p><p>An imaging campaign of a large sample of quasars at intermediate redshift (0.4 < z < 0.8) was carried out at optical wavelengths using the Nordic Optical Telescope, and is studied in this thesis together with two smaller samples. The joint material forms more than half of the total number of observed sources in this redshift interval and increases the number of resolved radio-quiet hosts at z>0.4 considerably. The morphology and mean magnitudes are found to be similar for radio-loud and radio-quiet host galaxies. Both types of host are shown to have optical colours as blue as those of present-day late-type spirals and starburst galaxies, which is likely the result of ongoing star formation.</p><p>With increasing redshift, observations of host galaxies become more difficult. High spatial resolution can be achieved with adaptive optics, but the variation of the point spread function in the near-infrared wavelength band which is most suited for detection is large and rapid. A statistical approach to the problem of characterizing the point spread function has been developed, making use of simulated objects which are matched to the different atmospheric conditions. Bright, compact host galaxies showing signs of merging and interaction were detected in this way for three quasars at z~2.2, which were observed with the ESO 3.6 m telescope. The method is not restricted to host galaxy analysis but can be utilized in other applications as well, provided that the underlying extended source can be described by an analytical model. </p>

Quasars form one of the most energetic phenomena in the universe, and can be traced out to very large redshifts. By studying the galaxies which host the active nuclei, important insights can be gained into the processes that trigger and maintain the quasar powerhouse. The evolution rate of the quasar population is furthermore similar to that of ordinary galaxies, which implies a connection between black hole accretion and star formation in the host galaxies. While the properties of quasar host galaxies at low redshift have become better constrained in recent years, less is known about hosts at earlier cosmic epochs. In addition, though radio-quiet quasars are by far more common than their radio-loud counterparts their host galaxies have not been studied to the same extent, in particular not at higher redshifts. An imaging campaign of a large sample of quasars at intermediate redshift (0.4 &lt; z &lt; 0.8) was carried out at optical wavelengths using the Nordic Optical Telescope, and is studied in this thesis together with two smaller samples. The joint material forms more than half of the total number of observed sources in this redshift interval and increases the number of resolved radio-quiet hosts at z&gt;0.4 considerably. The morphology and mean magnitudes are found to be similar for radio-loud and radio-quiet host galaxies. Both types of host are shown to have optical colours as blue as those of present-day late-type spirals and starburst galaxies, which is likely the result of ongoing star formation. With increasing redshift, observations of host galaxies become more difficult. High spatial resolution can be achieved with adaptive optics, but the variation of the point spread function in the near-infrared wavelength band which is most suited for detection is large and rapid. A statistical approach to the problem of characterizing the point spread function has been developed, making use of simulated objects which are matched to the different atmospheric conditions. Bright, compact host galaxies showing signs of merging and interaction were detected in this way for three quasars at z~2.2, which were observed with the ESO 3.6 m telescope. The method is not restricted to host galaxy analysis but can be utilized in other applications as well, provided that the underlying extended source can be described by an analytical model.

We present a detailed study of mid-infrared spectroscopy and optical imaging of Seyfert galaxies with the goal of understanding the properties of astronomical dust around the central supermassive black hole and the accretion disk. Specifically, we have studied Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8-1.9s and 58 Seyfert 1s and 2s available in the Spitzer public archive, and the nuclear dust morphology in the central 500 pc of 91 narrow and broad-line Seyfert 1s using optical images from the Hubble Space Telescope. We have also developed visualization software to aid the understanding of the geometry of the central engine. Based on these studies, we conclude that the nuclear regions of Seyfert galaxies are fueled by dusty spirals driven by the large-scale stellar bars in the host galaxy. The accumulation of dusty gas in the central kiloparsec leads to enhanced star formation. In this case, the circumnuclear starburst and the central engine compete for dominance in the heating of the circumnuclear dust. Emission from the heated dust is most clearly seen in the mid-infrared. We find that the spectra of Seyfert 2s show the most variety in the continuum shapes due to different starburst contributions. We find that the spectra of Seyfert 2s that are devoid of starburst contribution are dominated by a single thermal component at a temperature of T ~ 170 K. We also find that the mid-IR continua of Seyfert 1.8/1.9 galaxies are more like those of starburst-dominated Seyfert 2s than Seyfert 1s, contrary to expectations. We discuss the implications of these findings in the context of the Unified Model of AGN and the secular evolution of Seyfert nuclei.

The work in this thesis involves detailed multi-frequency radio continuum (from 325 MHz to 15 GHz) and Hi spectroscopic studies of a few represent tative nearby galaxies which are experiencing gas-loss from their disks due to different physical processes. These processes are starburst-driven superwind, active galactic nucleus (AGN) −driven nuclear outflow, ram pressure stripping and tidal interactions. Gas-loss could affect the evolution of individual galaxies with age as well as their evolution with cosmic epoch. We have made use of both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA) for our study. Stars and gases are the two major constituents of a galaxy. The properties of the gaseous medium in them change with galaxy-types, such as the presence of large amount of gas in the late type disk galaxies and little interstellar medium (ISM) in the ellipticals or early−type galaxies. Galaxies in groups and clusters interact with each other and with the low density gaseous medium surrounding them, resulting in a possible evolution of their structures and physical properties. Basic differences in their observed properties depend on their history of interactions with the environment and also on the history of their central activities. Tidal interaction among galaxies may result in the flow of gas into the central region of the galaxy. This can trigger a central starburst and/or feed a central super-massive black hole to trigger an AGN activity. These activities produce either starburst-driven superwind or AGN-driven nuclear outflows (accretion disk wind or bipolar radio jet/bubbles) and the galaxy may lose their metal-enriched central gas concentration to the intra-cluster (ICM) or intergalactic medium (IGM). There are suggestions that when large amount of gas is cleared out from the central region of an ultra-luminous infrared galaxy (ULIRG), the dust enshrouded hidden AGN may unveil itself as a bona fide quasi-stellar object (QSO). Galaxies also lose gas usually from the outer parts when they move through the intra-cluster medium (ICM) or intragroup medium (IGrM) due to ram pressure stripping. When the ram pressure is stronger than the pressure by which the gas is bound to the galaxy, most of the gas may be lost or displaced from the disk thus affecting the star formation and metal formation in the disk of the galaxy. Starburst galaxies and superwinds: The starformation rate or the supernovae rate in some gas rich galaxies are 10−1000 times higher than that of the normal galaxies. This process can consume large amount (1−30×109 M) of gas over a short time scale (107−8yr) in a small region (typically 1 kpc). During such bursts of starformation, the cumulative effect of many supernovae and stellar winds from the massive stars in the central region of a disk galaxy imparts huge amount of mechanical energy to the ISM of the galaxy which then creates a high pressure (4 orders of magnitude higher then the average ISM pressure in the Milky way), high temperature (106−7 K) bubble of gas. This high pressure and high temperature bubble of gas expands and flows outwards in the direction of the steepest pressure gradient. This outflowing hot gas carries cooler gas and dust from the ISM along with it. It carries out heavy metals cooked in the central region of a galaxy to the external environment including the ICM or IGM. The typical outflow rate is 10−100Myr−1 with typical outflow velocity of few 100−1500 km s−1and it persists over few to 10 million yr. The observed sizes of such outflows are 1−20 kpc. We have studied a remarkable starburst-superwind system, NGC1482. This early type galaxy has been discovered to have a bi-conical shaped soft X-ray outflow as well as Hα and [Nii] outflow. The low-frequency radiocontinuum flux density was used to estimate the supernova rate, which could be used to constrain the dynamics of the driving force. The high-frequency high-resolution VLA observations revealed the central starforming region which is at the base of the bi-conical structure and presumably driving this outflow. The Hi observations also have resulted in finding two blobs of Hi on opposite sides of the galaxy defining an axis perpendicular to the outflow axis and rotating about it. We have also detected a multi-component broad (∼ 250 km s−1) Hi-absorption spectrum against the central continuum source. The absorption spectrum is nearly 70 km s−1 asymmetric towards the blue side with a component blue-shifted by 120 km s−1. The observed absorption could be due to the Hi-clouds driven outward by the central superwind outflow. Active galaxies and nuclear outflows: The inflow of gas to the central region of a galaxy triggers the starformation as well as the AGN activity. Co-existence of both these phenomena in some cases are well known. The accretion disk of the AGN can produce a hot wind emitting in X-rays in addition to the radio continuum jet perpendicular to the accretion disk. It is known that the AGN jets, in particular Seyfert jets have no correlation with the rotation axis of the host disk-galaxy. In such a scenario a very complex geometry can arise. Radio jets may interact with the starburst-driven winds or winds from the accretion disk or with the clouds of ISM of the galaxy accelerating and ionizing the gas. Sometimes the mass outflow rate may be ten times the mass accretion rate necessary to fuel the AGN, suggesting heavy mass loading of these AGN outflows. Depending on the energy of the outflow processes gas may be ejected out of the gravitational field of the galaxy. We have studied a composite galaxy, NGC6764 with an AGN and a very young starburst with two episodes of starformation, one 3−5 and another 15−50 Myr ago. The high-resolution high-frequency radio-continuum obser- vations reveal a radio core and roughly bi-conical radio emission oriented along the major axis of the galaxy with a feature which could be a jet. The lower-resolution images show bi-polar radio bubbles oriented along the minor-axis of the galaxy. These edge-brightened radio bubbles are asymmetric in size, extent (north-south) and luminosity. There is an east-west asymmetry in the spectral index of the bubbles. In a representative sample of dozen such radio bubbles in nearby galaxies we find that invariably all of these have an AGN. Similar to few other galaxies in the sample we also found that the radio continuum bubbles in NGC6764 are well correlated with the Hα filaments extending along the minor-axis of the galaxy. The CO(J=2-1) and CO(J=1-0) flux density ratio is also higher at the tip of the bubbles. Molecular gas plumes are seen extending along minor axis and have components blue-shifted by 140 km s−1. Our high-resolution Hi observations also show an absorption component at the systemic velocity with a weak component blue shifted by 120 km s−1. We have discussed the possibility of the radio plasma ejected from the AGN being carried outwards along the minor-axis by the superwind created by the young circumnuclear starburst. That bubble of hot gas from the superwind mixed with the relativistic plasma from the AGN is interacting with the cooler Hi and molecular gas of the ISM and driving it outwards. This interaction which is possibly in an early phase of expansion is also giving rise to the outflowing Hα filaments in this interesting composite galaxy. Cluster galaxies and stripping processes: When a galaxy moves through the hot and dense ICM with velocities 1000 km s−1, the ram pressure exerted by the ICM can strip the loosely bound and more tenuous gas of the galaxy. As a result of this the dense molecular gas or the stars in the galaxy remain almost unaffected but the tenuous gas moving out of the galaxy’s gravitational field could reach the ICM. The fate of such stripped gas is not well constrained. Recently very long tails with sizes of 50−125 kpc have been discovered. Some of these are magnetised, some ionised, some neutral and some are million degree hot. These tails may cool and eventually form galaxies or may evaporate and mix with the ICM. They enrich the ICM with metals and magnetic fields. In some cases galaxies are known to have become as high as 90 % deficient in Hi in comparison to the corresponding field galaxy of same type, size and luminosity. In the cluster/group environment tidal interactions with other group/cluster members or the cluster potential well could also take place affecting the observed properties of the galaxy. In addition, tidal interactions could also facilitate the removal of gas by ram pressure due to the ICM or IGrM. NGC4438 which we have studied in detail is an archetypal example of a galaxy which has been severely affected by the cluster environment. This late-type galaxy in the central region of the Virgo cluster is known to have interacted with the northern companion NGC4435. We have unambiguously resolved the radio nucleus from the lobes of radio continuum emission, and have shown it to have an inverted spectrum confirming it to be the nucleus. The lobes are almost perpendicular to the central molecular or stellar disk which is seen nearly edge-on. Projected onto the plane of the sky the lobeaxis is roughly parallel to the direction of the ram pressure wind. The lobes are very asymmetric in its extent, size and luminosity. The lobes are shelllike in structure and are interacting strongly with the asymmetric ISM. In the region of interaction both Hα and soft X-ray emission shells are seen. We explore possible reasons for the asymmetry in the lobes which is unlikely to be only due to the asymmetry in the density of the ISM on opposite sides of the galaxy. On a larger scale we have imaged the diffuse lower-frequency radio-continuum emission 5 kpc away from the central region seen on the western side of the disk of the galaxy. This extended emission has flatter spectral index at higher frequencies which suggests it to be a mixture of thermal and non-thermal components. In this region Hα, soft X-ray, Hi, molecular gas and relativistic plasma (i.e. all phases of the ISM) have been detected. We have found a linear structure on the western side near the same region with mass of nearly 200 million M We have imaged the Hi−emission from the stellar disk for the first time. The Hi -velocity field shows that the extra-planar gas could be rotating slower then the disk as seen in cases of ram pressure stripping. At lower resolution we detect more Hi from the halo of the galaxy. The iso-velocity contours appear to curve towards the axis of rotation or direction of the ram pressure wind, as you go away from the mid plane. We discuss whether this might be due due to the interaction of NGC4438 with NGC4435. We have discovered a 50 kpc long faint tail of Hi having a mass of 140 million solar mass to the north-west of the NGC4438−NGC4435 system. This Hi−tail partially coincides with an extremely faint (µv> 28) stellar tail, which has been seen in the deep optical imaging of intra-cluster light. Such tails have not been predicted by the simulations of interaction between NGC4435 and NGC4438. Hence it seems to be a remnant of some past event in the evolution of this interesting system. To further study the effects of ram pressure stripping and tidal interaction in galaxies in a group, we have studied the group Ho 124. We found that the radio continuum bridge of tidal interaction between NGC2820 and NGC2814 has a very steep (α=−1.8) spectrum possibly due to the older relativistic plasma left in it. The Hi of NGC2820 has sharp truncation on the southeastern side parallel to the edge on disk, while it has a unipolar huge loop on the north-west. NGC2814 has both an Hi and radio continuum tail different from the connecting bridge with sharp truncation again on the side opposite to the tail. Although there is reasonable radio continuum emission from the disk of NGC2820, there is no detectable emission corresponding to the huge one sided Hi loop. The velocity field of the Hi-loop trails that of the underlying stellar disk. Also in the galaxy NGC2805, a member of the same group, we find the Hi to have accumulated on the northern side while there is a bow-shock shaped starformation arc on the southern side of the disk. All these features namely starformation arc, sharp cut off in the Hi-disk, Hi-loop and Hiand radio continuum tails are signatures of ram pressure stripping. Ram pressure stripping in groups is relatively rare but this could get assistance from tidal interactions which help loosen the gravitational bound of the stellar disk on the tenuous ISM. A more spectacular case of ram pressure stripping is seen in the cluster Abell 1367. We have studied a region of the cluster A1367 where three of its galaxies namely CGCG 09773, CGCG 09779 and CGCG 09787 exhibit amazingly long (50−75 kpc) tails of radio continuum and optical emission lines (Hα) pointing roughly away from the cluster centre. They also show arcs of starformation on the side facing the ram pressure of the cluster medium. In our Histudy we found that all three of them have higher mass of Hi on the down-stream side. Two of the galaxies (CGCG 09773 and CGCG 09779) exhibit sharper gradients in Hiintensity on the side of the tail or on the down-stream side. However the Hi emission in all the three galaxies extends to much smaller distances than the radio-continuum and Hαtails, and are possibly still bound to the gravitational pull of the respective galaxies. These results are in good agreement with the hydrodynamical simulations of ram pressure stripping in cluster medium. In this study we have found a number of interesting results on a few nearby galaxies where different gas-loss processes have modified the morphology and kinematics of the ISM and/or the stellar distribution of the respective parent galaxies. We have found evidence of blue-shifted Hi absorption lines driven outwards by the starburst-driven superwinds and/or AGN-driven nuclear outlows. The synchrotron plasma outflowing from an AGN in a composite galaxy has been suggested to be interacting with the superwind which also drives other components of the ISM outwards. In groups or clusters of galaxies we have discovered an Hiloop, Hitails, regions of compressed Hi, trailing velocity fields, slow-rotating extra-planar gas, displaced ISM and asymmetries in various radio continuum or Hifeatures as evidences of ram pressure stripping mechanism affecting the member galaxies. The results obtained from this study illustrates the manifestations of gas loss proceeses in galaxies existing in different environments, and should provide valuable insights for future investigations with larger statistical samples towards a more complete understanding of gas loss processes in galaxies and their implications on galaxy evolution