We present an analysis of high-resolution ALMA interferometry of CO(4-3) line emission and dust continuum in the "Ruby" (PLCK_G244.8+54.9), a bright, gravitationally lensed galaxy at z = 3.0 discovered with the Planck all-sky survey. The Ruby is the brightest of Planck's dusty GEMS, a sample of 11 of the brightest gravitationally lensed high-redshift galaxies on the extragalactic sub-mm sky. We resolve the high-surface-brightness continuum and CO line emission of the Ruby in several extended clumps along a partial, nearly circular Einstein ring with 1.4 '' diameter around a massive galaxy at z = 1.5. Local star-formation intensities are up to 2000 M-circle dot yr(-1) kpc(-2), amongst the highest observed at high redshift, and clearly in the range of maximal starbursts. Gas-mass surface densities are a few x10(4) M-circle dot pc(-2). The Ruby lies at, and in part even above, the starburst sequence in the Schmidt-Kennicutt diagram, and at the limit expected for star formation that is self-regulated through the kinetic energy injection from radiation pressure, stellar winds, and supernovae. We show that these processes can also inject sufficient kinetic energy and momentum into the gas to explain the turbulent line widths, which are consistent with marginally gravitationally bound molecular clouds embedded in a critically Toomre-stable disk. The star-formation efficiency is in the range 1-10% per free-fall time, consistent with the notion that the pressure balance that sets the local star-formation law in the Milky Way may well be universal out to the highest star-formation intensities. AGN feedback is not necessary to regulate the star formation in the Ruby, in agreement with the absence of a bright AGN component in the infrared and radio regimes.

We present a sample of similar to 1000 emission-line galaxies at z = 0.4-4.7 from the similar to 0.7deg(2) High-z Emission-Line Survey in the Bootes field identified with a suite of six narrow-band filters at approximate to 0.4-2.1 mu m. These galaxies have been selected on their Ly alpha (73), [O (II)] (285), H beta/[O (III)] (387) or H alpha (362) emission line, and have been classified with optical to near-infrared colours. A subsample of 98 sources have reliable redshifts from multiple narrow-band (e.g. [O (II)]-H alpha) detections and/or spectroscopy. In this survey paper, we present the observations, selection and catalogues of emitters. We measure number densities of Ly alpha, [O (II)], H beta/[O (III)] and H alpha and confirm strong luminosity evolution in star-forming galaxies from z similar to 0.4 to similar to 5, in agreement with previous results. To demonstrate the usefulness of dual-line emitters, we use the sample of dual [O (II)]-H alpha emitters to measure the observed [O (II)]/H alpha ratio at z = 1.47. The observed [O (II)]/H alpha ratio increases significantly from 0.40 +/- 0.01 at z = 0.1 to 0.52 +/- 0.05 at z = 1.47, which we attribute to either decreasing dust attenuation with redshift, or due to a bias in the (typically) fibre measurements in the local Universe that only measure the central kpc regions. At the bright end, we find that both the H alpha and Ly alpha number densities at z approximate to 2.2 deviate significantly from a Schechter form, following a power law. We show that this is driven entirely by an increasing X-ray/active galactic nucleus fraction with line luminosity, which reaches approximate to 100 per cent at line luminosities L greater than or similar to 3 x 10(44) erg s(-1).

We present a study of the relation between galaxy stellar age and mass for 14 members of the z = 1.62 protocluster IRC 0218, using multiband imaging and HST G102 and G141 grism spectroscopy. Using UVJ colors to separate galaxies into star-forming and quiescent populations, we find that, at stellar masses M*>= 10(10.85)M circle dot the quiescent fraction in the protocluster is f(Q) = 1.0(-0.37)(+0.00), consistent with a similar to 2x enhancement relative to the field value, f(Q) = 0.45(-0.03)(+0.03). At masses 10(10.2)M circle dot <= M* <= 10(10.85)M circle dot, f(Q) in the cluster is f(Q) = 0.40(-0.18)(+0.20), consistent with the field value of f(Q) = 0.28(-0.02)(+0.02). Using galaxy D-n(4000) values derived from the G102 spectroscopy, we find no relation between galaxy stellar age and mass. These results may reflect the impact of merger- driven mass redistribution-which is plausible, as this cluster is known to host many dry mergers. Alternately, they may imply that the trend in f(Q) in IRC 0218 was imprinted over a short timescale in the protocluster's assembly history. Comparing our results with those of other high- redshift studies and studies of clusters at z similar to 1, we determine that our observed relation between f(Q) and stellar mass only mildly evolves between z similar to 1.6 and z similar to 1, and only at stellar masses M* <= 10(10.85) M circle dot Both the z similar to 1 and z similar to 1.6 results are in agreement that the red sequence in dense environments was already populated at high redshift, z greater than or similar to 3, placing constraints on the mechanism(s) responsible for quenching in dense environments at z >= 1.5.

Our sensitive (sigma(n) approximate to 572 nJy beam(-1)), high-resolution (FWHM theta(1/2) = 0"22 approximate to 2 kpc at z greater than or similar to 1), 10 GHz image covering a single Karl G.. Jansky Very Large Array (VLA) primary beam (FWHM circle minus(1/2) approximate to 4.'25) in the GOODS-N field contains 32 sources with S-p greater than or similar to 2 mu Jy beam(-1) and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is <theta(M)>= 167 +/- 32 mas approximate to 1.2 +/- 0.28 kpc, with rms scatter approximate to 91 mas approximate to 0.79 kpc. In units of the effective radius re that encloses half their flux, these radio sizes are re approximate to 69 +/- 13 mas approximate to 509 +/- 114 pc, with rms scatter approximate to 38 mas approximate to 324 pc. These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected H alpha sizes. We made a lowresolution (theta(1/2) = 1."0) image with approximate to 10x better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices alpha(10 GHz)(1.4 GHz) 10 GHz. It contains six new sources with Sp. 3.9 mJy beam-1 and OIR counterparts. The median redshift of all 38 sources is similar to z similar to = 1.24 +/- 0.15. The 19 sources with 1.4 GHz counterparts have a median spectral index of <alpha(1.4 GHz) (10 GHz)> = -0.74 +/- 0.10 10 GHz, with rms scatter approximate to 0.35. Including upper limits on a for sources not detected at 1.4 GHz flattens the median to <alpha(1.4 GHz) (10 GHz)> greater than or similar to -0.61 10 GHz, suggesting that the mu Jy radio sources at higher redshifts-and hence those selected at higher rest-frame frequencies-may have flatter spectra. If the non-thermal spectral index is alpha(NT) approximate to -0.85, the median thermal fraction of sources selected at median rest-frame frequency approximate to 20 GHz is greater than or similar to 48%.

Recently acquired WFC3 UV (F275W and F336W) imaging mosaics under the Legacy Extragalactic UV Survey (LEGUS), combined with archival ACS data of M51, are used to study the young star cluster (YSC) population of this interacting system. Our newly extracted source catalogue contains 2834 cluster candidates, morphologically classified to be compact and uniform in colour, for which ages, masses and extinction are derived. In this first work we study the main properties of the YSC population of the whole galaxy, considering a mass-limited sample. Both luminosity and mass functions follow a power-law shape with slope -2, but at high luminosities and masses a dearth of sources is observed. The analysis of the mass function suggests that it is best fitted by a Schechter function with slope -2 and a truncation mass at 1.00 +/- 0.12 x 10(5) M-circle dot . Through Monte Carlo simulations, we confirm this result and link the shape of the luminosity function to the presence of a truncation in the mass function. A mass limited age function analysis, between 10 and 200 Myr, suggests that the cluster population is undergoing only moderate disruption. We observe little variation in the shape of the mass function at masses above 1 x 10(4) M-circle dot over this age range. The fraction of star formation happening in the form of bound clusters in M51 is similar to 20 per cent in the age range 10-100 Myr and little variation is observed over the whole range from 1 to 200 Myr.

We have identified 1027 star-forming complexes in a sample of 46 galaxies from the Spirals, Bridges, and Tails (SB&T) sample of interacting galaxies, and 693 star-forming complexes in a sample of 38 non-interacting spiral (NIS) galaxies in 8 μm observations from the Spitzer Infrared Array Camera. We have used archival multi-wavelength UV-to IR observations to fit the observed spectral energy distribution of our clumps with the Code Investigating GALaxy Emission using a double exponentially declined star formation history. We derive the star formation rates (SFRs), stellar masses, ages and fractions of the most recent burst, dust attenuation, and fractional emission due to an active galactic nucleus for these clumps. The resolved star formation main sequence holds on 2.5 kpc scales, although it does not hold on 1 kpc scales. We analyzed the relation between SFR, stellar mass, and age of the recent burst in the SB&T and NIS samples, and we found that the SFR per stellar mass is higher in the SB&T galaxies, and the clumps are younger in the galaxy pairs. We analyzed the SFR radial profile and found that the SFR is enhanced through the disk and in the tidal features relative to normal spirals.

Using archived data from the Chandra X-ray telescope, we have extracted the diffuse X-ray emission from 49 equal-mass interacting/merging galaxy pairs in a merger sequence, from widely separated pairs to merger remnants. After the removal of contributions from unresolved point sources, we compared the diffuse thermal X-ray luminosity from hot gas (L X(gas)) with the global star formation rate (SFR). After correction for absorption within the target galaxy, we do not see a strong trend of L X(gas)/SFR with the SFR or merger stage for galaxies with SFR > 1 Myr-1. For these galaxies, the median L X(gas)/SFR is 5.5 ×1039 ((erg s-1)/Myr-1)), similar to that of normal spiral galaxies. These results suggest that stellar feedback in star-forming galaxies reaches an approximately steady-state condition, in which a relatively constant fraction of about 2% of the total energy output from supernovae and stellar winds is converted into X-ray flux. Three late-stage merger remnants with low SFRs and high K-band luminosities (L K ) have enhanced L X(gas)/SFR; their UV/IR/optical colors suggest that they are post-starburst galaxies, perhaps in the process of becoming ellipticals. Systems with L K < 1010 L have lower L X(gas)/SFR ratios than the other galaxies in our sample, perhaps due to lower gravitational fields or lower metallicities. We see no relation between L X(gas)/SFR and Seyfert activity in this sample, suggesting that feedback from active galactic nuclei is not a major contributor to the hot gas in our sample galaxies.

Star formation occurs when the gas (mostly atomic hydrogen; H I) in a galaxy becomes disturbed, forming regions of high density gas, which then collapses to form stars. In dwarf galaxies it is still uncertain which processes contribute to star formation and how much they contribute to star formation. Blue compact dwarf (BCD) galaxies are low mass, low shear, gas rich galaxies that have high star formation rates when compared to other dwarf galaxies. What triggers the dense burst of star formation in BCDs but not other dwarfs is not well understood. It is often suggested that BCDs may have their starburst triggered by gravitational interactions with other galaxies, dwarf-dwarf galaxy mergers, or consumption of intergalactic gas. However, there are BCDs that appear isolated with respect to other galaxies, making an external disturbance unlikely. Here, I study six apparently isolated BCDs from the LITTLE THINGS1sample in an attempt to understand what has triggered their burst of star formation. LITTLE THINGS is an H I survey of 41 dwarf galaxies. Each galaxy has high angular and velocity resolution H I data from the Very Large Array (VLA) telescope and ancillary stellar data. I use these data to study the detailed morphology and kinematics of each galaxy, looking for signatures of starburst triggers. In addition to the VLA data, I have collected Green Bank Telescope data for the six BCDs. These high sensitivity, low resolution data are used to search the surrounding area of each galaxy for extended emission and possible nearby companion galaxies. The VLA data show evidence that each BCD has likely experienced some form of external disturbance despite their apparent isolation. These external disturbances potentially seen in the sample include: ongoing/advanced dwarf-dwarf mergers, an interaction with an unknown external object, and external gas consumption. The GBT data result in no nearby, separate H I companions at the sensitivity of the data. These data therefore suggest that even though these BCDs appear isolated, they have not been evolving in isolation. It is possible that these external disturbances may have triggered the starbursts that defines them as BCDs. 1Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey; https://science.nrao.edu/science/surveys/littlethings

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

In this thesis we test and expand our current knowledge of Star Formation Laws (SF laws) in the extreme environment of dwarf irregular galaxies. We focus on the SF characteristics of our 18 galaxies sample, extending current investigations of the Schmidt-Kennicutt law to the low luminosity, low metallicity regime. The Hi data used in this project have been observed, calibrated and imaged according to the LITTLE THINGS Survey prescription to which I brought my own contribution as a member of the team. Apart from high resolution, VLA data in B, C and D array configurations, this project makes use of an extensive set of multi- wavelength data (H , FUV, 24 m, 3.6 m, V-band and K-band). Molecular gas in dwarfs is very difficult to observe, mainly because due to the low metallicity environment, we lose our only molecular tracer, the CO which becomes under luminous. Therefore the gas distribution is represented by Hi gas only. We create our Star Formation Rate (SFR) maps mainly based on FUV maps because our analysis shows that FUV is the SF tracer that allows us the most extensive sampling of the SFR surface density (SFRD) and Hi surface density relation. The main results of our study are: Whereas in spiral galaxies Bigiel et al. (2008) have found a one to one relation between star formation rate and molecular gas and no relation between the SFR and the neutral gas, in a small sample of dwarfs as well as in the outskirts of spiral galaxies Bigiel et al. (2010b) has found that SFRD does correlate with Hi surface density. We confirm the existence of the SFRD vs. Hi surface density relation in dwarf irregular galaxies and a linear fitting through all our data (all 18 galaxies combined) yields a power law relation ΣSFR ∝ Σ1.87±0.3/HI . We find that the interiors of Hi shells, at 400 pc scales, become resolved and show up in SFRD versus Hi surface density plots although within the shell interior we have SFRD values but no Hi surface density related to them. Thus, the points originating from those regions contribute significantly to the increase of the scatter in the plot. We show that by excluding those points the correlation between SFRD and Hi surface density improves between 10% and 20%. Eight of the 18 galaxies in our sample have Hi maxima higher than the 10M pc-2 value found by Bigiel et al. (2008) for spiral galaxies. Krumholz et al. (2011) predicted that the 10M pc-2 threshold is metallicity dependent in galaxies with sub-solar metallicity, however the theoretically predicted values for our galaxies only match the observed Hi maxima in one case (DDO168). We find that metallicity cannot be the only factor setting the Hi to H2 transition. In fact, we find evidence that the higher the interstellar radiation field (ISRF), the higher the Hi maximum is, hence we suggest that the ISRF should also be taken into consideration in predicting the Hi to H2 transition threshold. We find that even tighter than the SFRD vs. Hi surface density relation is the SFRD vs. V-band surface density relation. Unlike the SFRD vs. Hi surface density relation the SFRD vs. V-band surface density relation follows a power law and can be written as follows: ΣSFR ∝ (10^μv)^-0.43±0.03. The SFRD vs. V-band surface density relation suggests that the existing stars also play a role in the formation of the next generation of stars. Within our sample of dwarf galaxies the average pressure per resolution element and the SFRD are in a 1:1 linear relation: ΣSFR ∝ P_h^1.02±0.05. A similar relation has been found by Blitz & Rosolowsky (2006) for the low-pressure regimes of spiral galaxies. In conclusion we find that in the extreme environments of dwarf galaxies the metal deficiency and the lack of the classic SF stimulators (spiral arms, shear motions) do not impede the star forming process. In these galaxies, dust-shielding becomes predominantly self-shielding and there is plenty of Hi available to achieve this additional task. Existing stars assume the role of pressure enhancers, which in turn will stimulate SF without the need of spiral arms or shear motion.